User's Handbook to the
#V^r#V D 1 400/800®
r^ I r\> IT LI computers
Jeffrey R. Weber
Stephen J. Szczecinski
>WEBER
I SYSTEMS
INCORPORATED
USERS HANDBOOK
TO THE
ATARI 400/800® COMPUTERS
by:
Jeffrey R. Weber
Stephen J. Szczecinski
Weber Systems, Inc.
Cleveland, Ohio
Published by:
Weber Systems, Inc.
8437 Mayfield Road
Cleveland, Ohio 44026
For information on translations and book distributors outside of
the United States, please contact WSI at the above address.
User's Handbook To The Atari 400/800® Computers
First Edition
Copyright© 1983 by Weber Systems, Inc.. All rights reserved.
Printed in the United States of America. No part of this
publication may be reproduced, stored in a retrieval system, or
transmitted in any form or by any means, electronic, mechanical,
photocopy, recording, or otherwise without the prior written
permission of the publisher.
Library of Congress Catalog Card Number 82-051088
ISBN 0-938862-15-4
Typesetting: Chelley Hoffman
Production & Design: Beth Cammarn
CONTENTS
1. INTRODUCTION TO THE ATARI COMPUTERS 7.
AND PERIPHERALS
Atari 400 and 800 7. Atari 800 Specifications 9.
Atari 400 Specifications 10. Atari Keyboard 11.
Atari Video Display 11. Plug-In Cartridge
Hatches 13. Computer Memory 13. Atari 410
Program Recorder 14. Atari 810 Disk Drive 15.
Atari Printers 16. Atari 850 Interface Module 16.
Game Controls 17. Software 17. Operating
Systems 17. Languages 18. Applications
Programs 18.
2. INSTALLATION AND OPERATION OF ATARI 19.
COMPUTERS
Introduction 19. Installing the Atari 400 21.
Installing the Atari 410 Recorder 21. Installing
the Atari 810 Disk Drive 21. Installing the Atari
820 Printer 23. Installing the Atari 822 Printer 24.
Installing the Atari 825 Printer 24. Installing a
ROM Cartridge 25. Power On 26. Keyboard 30.
System Reset Key 31. Select Key 31. Option Key
31. Start Key 31. Return Key 32. Break Key 32.
Shift Key 32. Ctrl Key 33. Caps/Lowr Key 33. A
Key 34. Arrow Keys 34. Back S Key 35. Clear
Key 35. Insert & Delete Keys 35. Tab Key 35. ESC
Key 36. Auto Repeat 36. Display Line Length 36.
3. INTRODUCTION TO ATARI BASIC 37.
Immediate & Program Modes 37. Line Numbers
38. NEW 40. END 40. Program Execution 40.
Program Lines & Display Lines 41. Multiple
Statement Program Lines 41. Abbreviating
Keywords 42. Listing a Program 42. Error
Messages 43. BASIC Data Types 44. Floating
Point Numbers 44. Scientific Notation 45. Tables
& Arrays 49. Expressions & Operators 51.
Compound Expressions & Order of Evaluation
52. Arithmetic Operations 53. Relational
Operators 55. Logical Operators 56. Atari
BASIC Statements 59. Remark Statements 59.
Assignment Statements 60. DATA, READ 60.
Outputting DATA 62. INPUT Statements
64. Loops 66. Nested Loops 67. Conditional
Statements 68. Branching Statements 68. ON,
GOTO 70. Subroutines & GOSUB Statements
70. ON, GOSUB 72. Break Key & CONT 72.
System Reset Key 72. STOP 73. END 73. Atari
BASIC Functions 74.
4. ADVANCED ATARI BASIC 75.
Atari ASCII 75. String Handling 76. Substrings
76. String Concatenation 77. CHR$ & ASC
Functions 78. Escape Sequences in Strings
79. Graphics Characters in Strings 80. Variable
Storage 82. PEEK & POKE 83. Screen Output
Programming 84. Using the Carriage Return in
Cursor Positioning 84. TAB 85. Moving the
Cursor With Escape Sequences 86. Home
Cursor 87. POSITION 87. Changing the Display
Screen Margins 88. Screen Input Programming
88. Prompt Messages 88. Input Response
Checks 89.
5. ATARI BASIC REFERENCE GUIDE 91.
ABS 92. ADR 92. AND 92. ASC 94. ATN
94. BYE 95. CLOAD 95. CHR$ 96. CLOG 96.
CLOSE 97. CLR 97. COLOR 98. COM 102.
CONT 103. COS 104. CSAVE 104. DATA 105.
DEG 106. DIM 107. DOS 110. DRAWTO 112.
END 114. ENTER 114. EXP 115. FOR 116. FRE
118. GET 119. GOSUB 123. GOTO 125.
GRAPHICS 126. IF 126. INPUT 129. INT 132.
LEN133. LET 133. LIST 134. LOAD 136. LOCATE
137. LOG 139. LPRINT 139. NEW 140. NEXT
141. NOT 142. NOTE 143. ON 144. OPEN 145.
OR 153. PADDLE 154. PEEK 155. PLOT 156.
POINT 157. POKE 158. POP 159. POSITION
160. PRINT 161. PTRIG166. PUT 166. RAD 169.
READ 170. REM 171. RESTORE 171. RETURN
172. RND172. RUN 173. SAVE 174. SETCOLOR
175. SGN 175. SIN 175. SOUND 176. SQR 177.
STATUS 177. STICK 178. STRIG 179. STOP 180.
STR$ 181. TRAP 181. USR 182. VAL 183. XIO
184.
6. ATARI 410 PROGRAM RECORDER 189.
Introduction 189. Data Files 189. Program Files
190. Saving Programs 190. Program Recording
Formats 191. Loading a Program 192. RUN C:
195. Reading and Writing Data 197. Opening
DataFiles198. Closing Data Files 200. Writingto
a Data File 200. Reading From Data Files 202.
7. ATARI 810 DISK DRIVE 205.
Types of Disks 205. Hard Disks 205. Winchester
Disk Drives 206. Floppy Diskettes 207. Tracks &
Sectors 208. Hard & Soft Sectors 209. Single &
Double Sided Diskettes 211. Diskette Density
211. Write Protection 212. Disk Files
213. Filename Match Characters 213. Atari DOS
215. Disk Buffer 217. Booting DOS 217. DOS
Menu 218. Disk Directory 220. Run Cartridge
222. Copy File 223. Delete File 227. Rename
File 228. Lock File 230. Unlock File 231. Write
DOS File 231. Format Diskette 232. Duplicate
Disk 233. Binary Save 234. Binary Load 236. Run
At Address 237. Create MEM.SAV 238.
Duplicate File 239. Saving BASIC Programs 240.
Loading a Program 242. Chaining Programs
243. Opening a Disk File 244. Closinga Data File
246. Writing to a Data File 247. Reading From a
Data File 248. NOTE and POINT 250.
8. ATARI PRINTERS 253.
LIST P: 253. LPRINT 254. PRINT# & PUT 255.
Printer Buffer 255. Printer Character Sets
255. Atari 825 Control Characters 256. Line Feed
258. Reverse Line Feed 258. Hald-Line Feed &
Reverse Half-Line Feed 259. Carriage Return
259. Underlining 259. Standard, Condensed, &
Proportionally Spaced Character Sets 260.
Backspace & 1-6 Dot Spaces 260.
9. ATARI GRAPHICS & SOUND 263.
GRAPHICS 263. GRAPHICS 263. Color
Registers & SETCOLOR 265. GRAPHICS 1 & 2
267. COLOR 272. PLOT 277. DRAWTO 278.
GRAPHICS 3 thru 8 278. POSITION 281.
LOCATE 282. PUT 283. XIO 283. Atari Sound
285.
APPENDIX A. Atari Error Messages 287.
APPENDIX B. Atari BASIC Reserved Words 294.
APPENDIX C. Atari ASCII Code Set 295.
APPENDIX D. Atari 400/800 Memory Map 301.
APPENDIX E. Atari PEEK & POKE Locations 306.
Index 315.
CHAPTER 1.
INTRODUCATION TO THE ATARI
COMPUTER AND PERIPHERALS
Introduction
In this book, we will describe the Atari home computers as well
as the peripherals that can be attached to them such as disk
drives, cassette recorders, and printers.
In the first chapter of this book, we will discuss the features of the
Atari 400 and 800 computers, the 410 Program Recorder, the 810
disk drive, game controls, and the various Atari printers. In the
second chapter, we will discuss the installation and operation of
the Atari 400 or 800 and its various peripherals.
In the third and fourth chapters, we will discuss programming
the Atari in Atari's version of the BASIC programming language.
The fifth chapter contains a reference guide to the various Atari
BASIC commands, statements, and functions.
In Chapters 6, 7, and 8, we will discuss the Atari Cassette
Recorder, Atari Disk Drive, and Atari printers in greater detail. In
Chapter 9, we will discuss the usage of graphics and sound on the
Atari 400 and 800.
Atari 400 and 800
There are two Atari computer models; the Atari 400 and the Atari
800 (pictured in Illustration 1-1).
The Atari 400 and 800 are very similar. Both models function the
same and follow the same set of instructions. The difference
between the Atari 400 and 800 lies in the fact that the 800 has
features that the 400 does not.
For instance, the Atari 800 's memory can be expanded, while the
8 User's Handbook to the Atari 400/800 Computers
memory of the Atari 400 is more or less fixed. Also, with the Atari
800, a video monitor can be used for video output as well as a
regular television set. With the Atari 400, only a regular television
set can be used for video output. A video monitor offers a more
detailed picture than a regular television set. Also, the Atari 800
has a typewriter style keyboard while the Atari 400 has a flat panel
with the keys outlined on it. Finally, the Atari 800 allows two
accessory cartridges to be plugged in, while the Atari 400 allows
only one.
However, the Atari 400 does have one major advantage-it costs
less than the Atari 800.
From hereon, we will refer to both the Atari 400 and 800
collectively as the Atari, unless a distincion between the two is
necessary. Whenever we refer to one model, the reader can
assume that the concept applies to the other model as well,
unless we specify otherwise.
Illustration 1-1. Atari 800 Computer
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Introduction to the Atari Computers and Peripherals 9
Atari 800 Specifications
The Atari 800 consists of a group of components which include
the following:
• Computer Console
• TV Switch Box
• AC Power Adapter
• Atari 800 Operator's Manual
• Atari BASIC Manual
• Atari BASIC Language
• Atari Educational System
The Atari 800 Console contains the central processing unit or
CPU, the operating system in ROM, 8K or 16K of RAM, and two
expansion slots for additional RAM. The Atari 800 console also
contains the keyboard, 2 cartridge slots, controller jacks, and a
serial I/O port.
The TV switch box allows a regularTVsetto be used as the Atari's
video display. The AC power adapter converts regular AC
current to a low voltage that can be used by your Atari. The AC
power adapter can be plugged into any normal household
outlet.
The Atari Educational System and Atari BASIC language are
contained in two cartridges. Operator's instructions are
included with each of these.
The Atari 410 program recorder allows the use of programs
which have been stored on cassette tape. The Atari 410 also
allows the user to save his programs from RAM onto cassette
tape for later use.
The Atari 800's software is known as the operating system and is
contained on a 10K ROM cartridge. The operating system
controls the entire flow of information within the computer.
As shown in Illustration 1-2, the side panel of the Atari 800
contains several switches and jacks. The monitor jack can be
used to connect a video display monitor or a video tape
10 User's Handbook to the Atari 400/800 Computers
Illustration 1-2. Atari 800 Side Panel
recorder to your Atari 800.
The Atari 410 Program Recorder, Atari 810 disk drive, and Atari
820 printer are all installed by plugging into the peripheral jack.
More than one device can be connected through the peripheral
jack via a daisy chain configuration, where all devices to be used
are connected together. This is explained in more detail in
Chapter 2.
The 2-3 channel switch should be set to the same channel as the
television set being used for video output. Use channel 2 or 3,
whichever has the poorer reception.
The Atari 800 contains four controller jacks located in the front of
the console beneath the keyboard. These can be used for
connecting game controllers or a light pen.
Atari 400 Specifications
Your Atari 400 includes the Atari 400 console, as well as a TV
switch box, operator's manual, and an AC Power Adapter.
Introduction to the Atari Computers and Peripherals 11
The Atari 400 console contains the CPU, operating system in
ROM , 8K or 16K of RAM, one cartridge slot, controller jacks, and
one I/O connector.
The TV switch box allows a regular TV set to be used for video
output for the Atari 400. The AC power adapter converts
household current to a low voltage that can be used by the Atari.
Atari Keyboard
The Atari keyboard allows the user to interact with the
computer. The instructions entered at the keyboard are
transfered to the computer. The keys on both the Atari 400 and
800 are arranged in the same order as on a regular typewriter.
However, the Atari keyboard contains several special keys not
found on a standard typewriter keyboard. These keys will be
discussed in Chapter 2.
As mentioned in the previous section, the Atari 800's keyboard
features a typewriter style keyboard with raised keys. The Atari
400 keys are identified on a flat panel on the front of the unit.
Atari Video Display
Generally, a home color television set is used as the video display
screen for the Atari. A black and white television set can also be
used, in which case, the different colors will appear as various
shades of gray.
The Atari 800 allows the use of a video monitor as well as a
television set as its video display unit. A video monitor (either
color or black & white) tends to cause images to be displayed in
greater detail than a television set.
A television set is connected to the Atari computer with a switch
box that is itself connected to the television's antenna terminal.
This is shown in Illustration 1-3. The switch box has two
positions. One position allows the set to be used with the Atari,
while the other allows the set to function as a televison.
If a video display monitor is being connected to the Atari 800, a
12 User's Handbook to the Atari 400/800 Computers
switch box is not necessary. This connection can be
accomplished by attaching the 5-pin plug into the socket on the
side of the Atari 800. This is shown in Illustration 1-4.
Regardless of whether a television set or a monitor is being
connected to the Atari, several different modes of display are
available. One of these is the monochromatic text mode. This
mode is used to display one color plus white (ex. black and
white, blue and white, etc.). In the monochromatic text mode,
the screen is divided into 24 lines of 40 characters each. Two
other modes are available for displaying text in up to four
different colors. Other modes are available for displaying
graphics. These will be discussed in detail in Chapter 9.
Illustration 1-3. Atari/Television Set Hook-Up
Introduction to the Atari Computers and Peripherals 13
Illustration 1-4. Atari 800/Video Display Monitor Hook-Up
Plug-In Cartridge Hatches
Both the Atari 400 and 800 have a hatch on the top of the unit
which can be opened for the purpose of inserting a plug-in
cartridge (see Illustration 1-1). These cartridges contain ROM
memory (discussed later) on which programs are stored. These
programs may be games, applications programs, or even a BASIC
language interpreter.
The Atari 400 allows the insertion of a single cartridge while the
800 allows two cartridges to be inserted.
Computer Memory
Computer memory is measured in units known as bytes. A byte
is used to store a single character in the computer's memory.
Bytes are represented in units of measurement known as
14 User's Handbook to the Atari 400/800 Computers
kilobytes or K. IK is the equivalent of 1024 bytes. Your Atari may
contain from 18 to 60K of memory (or 18,432 to 61,440 bytes).
Computer memory can be one of two different types; ROM or
RAM. ROM stands for read-only memory. ROM will hold the
data stored in it permanently. If the power to the Atari is shut off,
the information stored in ROM will remain there. ROM contains
the programs that are used to operate the Atari, and allow it to
interact with the user.
RAM stands for random-access memory*. The data stored in
RAM can be changed. Applications programs are often
transferred from diskettes or cassette to RAM. Any data stored in
RAM is lost when the Atari's power is turned off.
The Atari 400 includes 16K of RAM. Generally, it is not advisable
to attempt to expand the RAM capacity of an Atari 400.
The Atari 800 allows RAM to be expanded from 16K to as much as
48K. RAM is expanded on the Atari 800 by inserting additional
RAM plug-in modules underneath the unit's top cover.
Expanding the Atari's RAM is explained in more detail in
Chapter 2.
Atari 410 Program Recorder
Cassette tape can be used to store programs in RAM and then
transfer these programs back into RAM at some later date. The
Atari 410 Program Recorder (as shown in Illustration 1-5) is
designed for use with the Atari computer. Approximately 50K or
51,200 bytes of data can be stored on a 30 minute cassette.
*Random access memory is a somewhat misleading term to
describe, RAM, as most memory (including ROM), is randomly
accessed.
Introduction to the Atari Computers and Peripherals 15
Illustration 1-5. Atari 410 Program Recorder
Atari 810 Disk Drive
A disk drive is a much more efficient device for storing data than
a cassette recorder. A disk drive allows greater storage capacity,
quicker access to data, as well as fewer errors in data transfers.
The Atari 810 disk drive (as shown in Illustration 1-6) is designed
to be used with Atari computers. The Atari 810 uses single-sided
single density diskettes.
Diskettes which are designed to be written on only one side are
known as single sided (SS) diskettes. Diskettes designed to be
written on both sides are known as double sided (DS) diskettes.
Density refers to a diskette's recording format, which in turn
affects its capacity. Single-sided single density diskettes (as used
with the Atari 810) have a capacity of approximately 94K.
16 User's Handbook to the Atari 400/800 Computers
Illustration 1-6. Atari 810 Disk Drive
V-... „.,..,,,
The Atari 810 disk drive can only be used with the Atari 800
computer with a minimum of 16K of RAM.
Atari Printers
Atari produces three different printers; the 820 Printer, 822
Thermal Printer, and 825 Wide Carriage Printer.
The 820 and 822 Printers are connected to the Atari computer via
the I/O Data Channel. The 825 Printer is connected to the Atari
computer with the 850 Interface Module. The 850 Interface
Module can be used to connect printers other than the 825 to the
Atari.
Atari 850 Interface Module
The Atari 850 Interface Module allows communications between
Introduction to the Atari Computers and Peripherals 17
the Atari computer and RS-232-C peripherals. We already
discussed the fact that the Atari 825 printer should be connected
via the Atari 850 Interface Module.
Another Atari peripheral that must be connected via the Atari
850 Interface Module is the Atari 830 Modem. The Atari 830
Modem allows your Atari to communicate with another terminal
also equipped with a modem over telephone lines.
The Atari 850 Interface Module is connected to the Atari
console. In turn, the peripherals are connected to the 850
Interface Module. The 850 Interface Module has 4 serial ports
and 1 parallel port, known as the printer port. The 850 Interface
Module has its own memory and processor and is programmed
from the Atari computer.
Came Controls
Three types of game control devices can be used with the Atari;
joysticks, paddles, and keyboard controllers.
Software
Software can be described as the instructions or programs that
cause the computer to operate. Several different classifications
of software exist for the performance of different functions.
These can be classified as operating systems, languages, and
applications programs.
Operating Systems
An operating system can be defined as a group of programs
which manage the overall operation of the computer. The
operating system performs system operations such as the
loading and unloading of data from cassette or diskette into
RAM and the display of operator keyboard entries on the video
screen.
18 User's Handbook to the Atari 400/800 Computers
The Atari's operating system is stored permanently in ROM. The
operating system is contained in a plug-in module in the Atari
800.
Languages
Programs are generally written in a high-level language that is
different from the instructions the computer uses. A program
known as an interpreter must be used to translate the high-level
language into a form that the computer can comprehend.
BASIC is the high-level language generally used with the Atari.
The Atari BASIC interpreter is contained on a ROM cartridge
which can be plugged in under the hatch of either the Atari 400
or 800.
Applications Programs
Applications programs are those written to accomplish a specific
task. Examples of applications programs are games, word
processing programs, financial forecasting programs, and
accounting programs. Generally, applications programs are
stored on cassette or diskette and are transferred into RAM,
where the program is available to the computer.
Applications programs for the Atari can also be stored in a
permanent form on a ROM cartridge. This ROM cartridge can
be plugged in underneath the hatch on the Atari. Examples of
ROM plug-in cartridges are shown in Illustration 2-4.
CHAPTER 2.
INSTALLATION AND OPERATION OF
ATARI COMPUTERS
Introduction
If you are a first-time computer user, your Atari may seem a little
confusing at first. However, using a computer is really very
simple. In this chapter, we hope to show you exactly howsimple
your Atari is by showing you step-by-step how to install and
operate it.
Installing the Atari 800
First of all, when you unpack your Atari 800, save the carton and
packing material. These should be used if the Atari is to be
moved or stored.
The Atari 800 is easy to install. First of all, install either a video
monitor via the monitor jack on the side of the console or a TV
set using the TV switch box.
The TV switch box has been designed so that it can be
permanently installed on your TV set, as it allows regular TV
reception as well as video output for the Atari. TheTV switch box
has an adhesive backing that can be used to attach it to the back
of your TV set.
The TV switch box contains a switch marked Computer/TV.
When this switch is at the Computer position, the TV set receives
its signals from the Atari 800. When the switch is set to the TV
position, the TV set receives its signals from your television
antenna.
To install the TV switch box, first of all, disconnect your television
antenna from the VHF terminals at the back of yourTV set. The
antenna should be either of the following:
20 User's Handbook to the Atari 400/800 Computers
• 75 OHM with screw-on connector
• 300 OHM with two flat leads
Attach either the 75 OHM or 300 OHM connector to the
matching connector on the side of the TV switch box.
Next, attach the 300 OHM connector (with the two flat leads)
leading from the bottom of the TV switch box and labeled TV, to
the VHF terminals on your TV set.
If your television antenna is a 300 OHM model, the TV switch box
installation is finished. If your antenna is a 75 OHM model, you
must convert your television to accept a 300 OHM signal from
the TV switch box.
Refer to Illustration 2-1. If the antenna box contains a switch as
shown in the top drawing, just push the switch to the 300 OHM
position. If the antenna box resembles that shown in the middle
drawing, loosen the screws holding the U-shaped slider, and
move it to the 300 OHM position. If the antenna box resembles
the last drawing, screw the round wire into the connector as
pictured.
Illustration 2-1. Television Set Conversion to 300 OHM
If your TV set resembles this
drawing, push the switch to the
300 SL position.
If your TV set resembles this
drawing, loosen the screws and
move the slider to the 300 SL
position.
If your TV set resembles this
drawing, screw the rounded
wire into the connector.
Installation and Operation of Atari Computers 21
Once the TV switch box has been connected, plug the AC power
adapter into any ordinary 115V household outlet. Plug the end of
the AC power adapter into the power jack on the side of the
Atari console. Then, follow the power-on procedures as
described later in this chapter.
Installing The Atari 400
The installation procedures for the Atari 400 are virtually
identical to those for the Atari 800. Follow the steps just outlined
for Atari 800 installation if you are installing an Atari 400.
Installing The Atari 410 Program Recorder
The Atari 410 Program Recorder is packaged with a power card
and a peripheral data card, which is permanently attached to the
recorder.
Use caution when using the Atari 410. Do not use the Atari 410
outdoors. Also, do not allow liquids to be spilled on the Atari 410,
or allow it to be dropped in water.
The first step in installing the Atari 410 is to plug the data card
(which is permanently attached to the 410) to the peripheral jack
on the side of the Atari's console. Next, plug the recorder's
power card into the AC jack on the side of the recorder, and plug
it into a household outlet.
Installing The Atari 810 Disk Drive
The Atari 810 will include the following:
810 Disk Drive
Data Cord (round card with
identical end plugs)
AC Power Adapter
Owner's Manual
DOS Diskette
22 User's Handbook to the Atari 400/800 Computers
Save the 810's carton and packing material, should the unit need
to be moved or stored.
Before installing the Atari 810 disk drive, be certain that the
power switches on both the Atari 810 and the computer are off.
The first step in installing the Atari 810 is to plug one end of the
AC power adapter into a household outlet, and the other to the
Atari 810 console. This is shown in Illustration 2-2.
Illustration 2-2. Installing the Atari 810
Installation and Operation of Atari Computers 23
Next, plug one end of the data cord to the peripheral plug on the
Atari console, and the other to one of the I/O connectors on the
rear of the Atari 810. This is shown in Illustration 2-2. Additional
peripherals can be connected via the unused I/O connector.
If just one disk drive is being installed, the device code switch in
the back of the Atari 810 should be set to 1. If 2, 3, or 4 drives are
to be installed, the swtiches should be set as indicated on the
drive code diagram on the back of the Atari 810. This is shown in
Illustration 2-5. Use a pen or screwdriver to move the switches to
the appropriate setting. Be certain that the power to the Atari 800
and 810 is off when setting the drive code switch.
Installing the Atari 820 Printer
The Atari 820 Printer includes the following items:
• Printer
• Roll of Paper
• Paper Mandrell
• Ribbon
• Data Cord
• User's Manual
• Attached Power Card
Never operate a printer without the ribbon and paper installed.
Doing so may cause damage to the printing head solenoids. The
instructions for loading the ribbon and the paper in the Atari 820
are given in the operator's manual.
Once the Atari 820 has been loaded with paper and a ribbon has
been installed, plug the power cord attached to the unit into a
household outlet.
Next, plug one end of the data cord into the port labeled
'peripheral' on the Atari computer console. If another
peripheral such as the Atari 810 Disk Drive has already been
installed via the peripheral port, the Atari 820 can be connected
via the I/O CONNECTOR port on the Atari 810 disk drive. Plug
the other end of the data cord into either of the I/O
CONNECTOR ports on the printer.
24 User's Handbook to the Atari 400/800 Computers
The printer is now installed. Turn the printer's power switch on
and press the paper advance button once. The printer is now
ready for paper to be loaded.
Installing the Atari 822 Printer
The installation procedure for the Atari 822 printer is essentially
the same as for the Atari 820 printer.
Installing the Atari 825 Printer
The Atari 850 Interface Module is required to install the Atari 825
printer to either the Atari 400 or 800. The Interface Module
converts serial data from the computer into parallel data used by
the Atari 825.
The installation procedure for the Atari 825 is depicted in
Illustration 2-3. A few words of caution are in order before
beginning installation. First of all, the Atari 825 should be
installed at a distance of at least 2 feet from your television set.
Secondly, be certain that all of the power switches on both the
Atari 825 and Atari 400 or 800 are turned off prior to installation.
Finally, note that the Atari 825 is delivered with a ribbon
installed. During installation, try to keep the Atari 825 level.
Otherwise, the ribbon may fall out of its tray.
Illustration 2-3. Installing the Atari 825 Printer
□
ATARI 400 or 800
ATARI 850
Interface Module
Caution: Be certain to install the
Atari 825 at a distance of at least 2
feet from the TV set or monitor.
ATARI 825 Printer
Installation and Operation of Atari Computers 25
Once these precautions have been taken, use an Atari I/O Data
Cord to connect the Atari 400 or 800 to the 850 I nterface Modu le.
Connect an AC adapter to the Power In jack on the 850 Interface
Module. Connect the other end to a regular household AC
outlet.
Connect the 3 prong power cord on the Atari 825 printer to an
outlet. The Edge-on connector of the Atari printer cable should
be connected to the printed circuit card connector on the back
of the printer. The side of the connector marked This side up'
should be facing up when the connection is made. Do not
attempt to force this connector, as this could damage the cable
connector. Connect the other end of the printer cable to the
parallel bit printer interface connection on the 850 Interface
Modules.
The 850 I nterface Module must be turned on before the Atari 825
can be used. Programming procedures for the Atari 825 will be
covered in Chapter 8.
Installing a ROM Cartridge
As discussed in Chapter 1, the ROM cartridges are installed
under the hatch cover on the top of the Atari. The Atari 400 has
one socket, while the Atari 800 has two.
Generally, cartridges are installed in the left slot. When inserting
a cartridge, hold it so that its label is facing towards you. Plug the
cartridge into the socket and press it all the way into the socket.
Finally, close the hatch. This is shown in Illustration 2-4.
When the Atari is operated without a cart ridge installed, it will be
operating in the memo pad mode. In this mode, all the Atari can
do is display what has been entered at the keyboard. Obviously,
the memo pad mode is not very useful.
In our discussions in this book, we will assume that the BASIC
Computing Language ROM cartridge is installed.
26 User's Handbook to the Atari 400/800 Computers
Illustration 2-4. Installing a ROM Cartridge
SlSISlllPP^PSlili&i
Turning on the Power
Once your Atari system has been properly installed, you may
turn on its power. Use the following procedure in turning on the
various components of your Atari system.
1. Turn on the television or monitor. If you are using a
television set, be certain both the set and the Atari are both
turned to the same channel. The switch connected to the
television set should be placed on computer.
2. If you are using the Atari 810 disk drive, turn on drivel and
insert a diskette with the Atari disk operating system (DOS)
on it. Close the drive door once the diskette has been
inserted.
3. If a serial device that has been connected to the 850
Interface Module is to be used, turn on the850. Otherwise,
leave it turned off.
Installation and Operation of Atari Computers 27
4. Turn on the Atari 400 or 800 console unit.
5. Turn on the printer when you wish to use it. Remember, if
you are using the 825 printer, the 850 Interface module
must also be turned on.
Unless the preceding power-on procedure is followed, the Atari
may not be able to interact with some of the system components.
Step 1. Turning on the Television
First of all, turn on the television set or monitor, whichever your
system is using. If you are using a monitor, you can skip the
remainder of Step 1 and proceed to Step 2.
If you are using a television set, first of all be certain that the
switch that is connected to your television's antenna terminal is
set to computer. Tune in your set to channel 2 or 3, whichever is
weaker in your area.
The Atari computer must be set to broadcast on the same
channel that the television is tuned to. This is accomplished with
the switch on the side of the Atari (see Illustration 1-2). Set this
switch so that it corresponds to the television channel used (2 or
3).
Step 2. Turning on the Disk Drive
If your system does not include a disk drive or if the disk drive
will not be used, you need not turn it on and can skip to Step 3.
If the disk drive is to be used, turn on drive 1. When turned on
the drive will emit whirring and clicking sounds for a few
seconds, and the lights on its front panel will light. The sounds
will soon stop, and all lamps except for the power lamp will go
off.
If your Atari system contains more than 1 drive, only drive 1
needs to be turned on at this point. By examining the access hole
in the back of the 810 drive (see Illustration 2-5), the user can
determine which is drive 1.
28 User's Handbook to the Atari 400/800 Computers
The access hole will contain one or two switch levers. The
position of these levers determines the drive number. Drive 1's
levers are both positioned to the left. Only the black lever in
front may be visible, at it may be hiding the white lever which is
situated behind it.
Illustration 2-5. Determining the Disk Drive Number
Once you have determined which drive is drive 1, insert either
the 'Disk File Manager Master Copy', a 'Disk File Manager II
Master Copy', or a copy of one of these in that drive. The label
side of the diskette should be facing up. Slide the diskette all the
way in and close the door behind it.
Step 3. Turning on the 850 Interface Module
The 850 Interface Module only needs to be turned on if a device
is attached to it. If not, you can leave it off.
Step 4. Turning on the Atari 400/800
You now are ready to turn on the heart of your Atari system— the
Atari 400 or 800 computer. First of all, be certain that the correct
ROM cartridge has been installed, and that all system
Installation and Operation of Atari Computers 29
components have been properly connected.
Now, locate the power-on switch on the side of the console as
shown in Illustration 1-2. Turn the switch to the on position, and
turn up the volume on your television set a little.
The power lamp on the keyboard should come on. Also, your
television set will begin making noises, and a blue field with a
black border will be displayed. If the disk drive is on, it will begin
to whirl.
Finally, the message, READY, will be displayed in white letters on
the screen, and the disk drive will stop whirling.
If the READY message is not displayed within 3 seconds, a
problem exists somewhere in the system. Be certain the
components of your system are properly connected, and that
the proper ROM cartridge is in place. Repeat the start-up
procedure. If the Atari still does not start, call your dealer for
assistance.
If the following message appears on the display:
BOOT ERROR
the problem probably lies with the disk drive. Be certain that a
DOS diskette has been installed label side up, and that the disk
drive door is closed.
Step 5. Turn on the Printer
Once Steps 1 through 4 have been accomplished, the printer
may be turned on as desired. Of course, printing operations can
not be undertaken unless the printer is on. Remember, the 825
printer requires that the 850 Interface module be on.
The Ready Message
Once the Ready message appears on the display, the Atari
computer is ready to accept commands entered by the user via
the keyboard. Just beneath the READY message, a white square
30 User's Handbook to the Atari 400/800 Computers
known as the cursor will be displayed. The cursor indicates the
position where the next character typed in will appear on the
display.
Atari Keyboard
As mentioned in Chapter 1, the Atari 400 and 800 keyboards are
virtually identical, except that the Atari 800 keyboard contains a
typewriter style keyboard with raised keys while the Atari 400
keyboard is depicted on a flat panel. The keyboard layout of the
Atari keyboard is shown in Illustration 2-6.
The Atari keyboard contains many of the same keys arranged in
the same order as a regular typewriter keyboard. The Atari
keyboard also contains several additional keys not found on a
typewriter keyboard. Two of these, ESC and CTRL, are
located on the left side of the keyboard. Three other keys,
BREAK, CAPS/LOWR, and A, are located on the right side of the
keyboard. Also, to the far right of the keyboard are four yellow
special function keys. Finally, some of the standard typewriter
keys contain special words or special symbols.
Illustration 2-6. Atari Keyboard
Installation and Operation of Atari Computers 31
In the next 17 sections, we will discuss the usageof all of the keys
on the Atari keyboard. We recommend that you experiment
with these keys as you read these sections. Do not worry about
damaging thecomputer. Any error situation caused by keyboard
entries can be corrected by merely turning the Atari off and then
on again.
System Reset Key
fcach of the four keys located to the right of the keyboard allows
the user to select a different starting position within a cartridge.
The System Reset key is located at the top of the yellow function
keypad at the far right of the keyboard. When the System Reset
key is pressed, all computer operations stop, and control is
restarted from the beginning of a cartridge.
Be careful not to press System Reset accidentally. Doing so can
cause the loss of data— especially if the disk drive is in use when
System Reset is pressed.
Select Key
Pressing the select key allows the user to view the initial screen at
the start of the next game or program. In other words, the initial
screen is 'selected'.
Option Key
The option key is pressed to record the user's choice of one of a
number of options within an application program or game.
Start Key
The Select and Option keys are generally used to display a screen
and record the user's choice. The next step is for the user to press
the start key. This begins the action selected.
32 User's Handbook to the Atari 400/800 Computers
Return Key
As characters are entered via the keyboard, these characters are
displayed on the video screen and also saved in memory.
However, these characters are not actually interpreted by the
computer until the Return key has been pressed. The Return key
tells the Atari that the line into which characters are being typed
has been finished.
When Return is pressed, the Atari will review the line just
entered for errors. If any errors are found, an error message will
be displayed.
Break Key
The Break key will stop any action being undertaken by the
computer. For example, if you press Break while entering a
BASIC command line, the computer will ignore all data entered
on the current line.
Pressing Break may or may not affect a program depending upon
how that program is written. Some programs are written so that
pressing Break has no effect, while other programs may stop if
Break is pressed. Generally, if a program is interrupted by
pressing Break, it can be continued by typing in the BASIC
command CONT and then pressing Return. However, the
display screen will most likely be erased if Break is pressed
during program execution.
Shift Key
Upon start-up, the keys for the letters (A-Z) always produce
upper case letters on the Atari, regardless of whether the Shift
key is depressed or released. However, the position of the Shift
key does have an effect on many of the other keys on the Atari
keyboard.
The keys affected by the position of the Shift key include two
characters. The bottom character is output when the Shift is off
(Unshift), and the top character is output when the Shift is on
(Shift).
Installation and Operation of Atari Computers 33
In this book, we will denote a key produced in theShift mode by
using the word Shift followed by the symbol or name of the
character produced in Unshift. For instance, Shift 9 would
denote the symbol (. The characters produced in the Shift mode
are listed in Appendix C.
Ctrl Key
Ctrl is an abbreviation for the word 'control'. We will use Ctrl and
Control interchangeably in this text.
The Control key is used in combination with another key much
as the Shift key is. The Control key must be held down at the
same time as the other key.
The use of the Control key with another key will be symbolized
by prefixing the name of that key with Ctrl-. For example, Ctrl-C
designates pressing the Control and C keys simultaneously.
Like the shift key, the Control key gives the key it is used with a
different interpretation. Control is used with the letter keys to
output the graphics characters. Control is used with many of the
other keys to instruct the computer to undertake a particular
function. For example, Ctrl-+ results in the cursor being moved
one space to the right. The various control key functions are
listed in Appendix C.
Caps/Lowr Key
As mentioned earlier, upon start-up, the keys for the letters (A-
Z) always produce upper case or capital letters, regardless of
whether the Shift key is depressed or released. The Caps/Lowr
key allows both capital and lower case letters to be output.
To output both capitals and lower case letters, press the
Caps/Lowr key. When the Shift key is released, lowercase letters
will be output. When the Shift key is depressed, upper case
letters will be output.
By pressing the Shift key and the Caps key simultaneously, the
Atari will again output upper case letters.
34 User's Handbook to the Atari 400/800 Computers
The keyboard can be placed in the graphics character mode by
pressing the Control and Caps/Lowr keys together. The graphics
characters are pictured in Appendix C.
JKKey
The>N. key is used to switch the keyboard between the normal
and the reverse video modes. In the reverse video mode,
characters are displayed in blue on a white background.
Arrow Keys
The arrows keys will be referred to as follows in this text.
Up Arrow — *-Ctrl-
Down Arrow — ►-Ctrl =
Left Arrow — ^Ctrl +
Right Arrow — »-Ctrl*
As you can see, the arrow keys are actually Control key
combinations.
The arrow keys are generally used to move the cursor on the
screen, so that keyboard entries can be corrected where
necessary.
The Right and Left Arrow keys move the cursor to the right or left
by one position along the same display line. These do not erase
the characters that they pass over from the display. When the
Right Arrow key is pressed with the cursor at the far right edge of
a display line, the cursor will move to the left edge of the same
line. When the left Arrow key is pressed with the cursor at the far
left side of the display, the cursor will move to the far right side.
The Up and Down Arrow keys move the cursor up or down by
one line. If the cursor is at the top of the screen, Up Arrow places
the cursor at the bottom of the screen. If the cursor is at the
bottom line of the screen, Down Arrow places it at the screen's
top.
Installation and Operation of Atari Computers 35
Back S Key
The Back S key moves the cursor one position to the left each
time it is pressed. The character beneath the cursor is erased
when Back S is pressed.
When the cursor is at the left edge of the screen and Back S is
pressed, the cursor will not move.
Clear Key
Either the Shift < orCtrl< key combination can be used to clear
the display screen and move the cursor to the home position.
The home position is the upper left-hand corner of the screen.
Insert and Delete Keys
Characters can be inserted or deleted by using the Control or
Shift keys in combination with the >/lnsert and Back S/Delete
keys. Ctrl> results in a blank space being inserted to the right of
the cursor. Ctrl Back S results in the character to the immediate
right of the cursor being deleted. The cursor does not move
when either Ctrl> or Ctrl Back S are pressed.
Shift >■ results in a blank line being inserted above the line that
the cursor currently is in. The remainder of the display below the
line the cursor is in moves down by one line.
Shift Back S causes the line that the cursor is currently in to be
erased from the screen. The lines beneath that line are shifted
upward in the display by one position.
Tab Key
When the Tab key is pressed, the cursor will move forward to the
next tab position on the screen. Standard tab positions occur
after every eight positions. The left margin on the Atari is
indented two columns from the screen's edge. Because of this,
the first tab stop occurs at the sixth position from the left margin.
Additional tab positions can be set by pressing Shift Tab at the
36 User's Handbook to the Atari 400/800 Computers
position desired. Pressing Ctrl Tab clears the tab stop at the
cursor's current position.
ESC Key
ESC is an abbreviation for Escape, a term originally used with
teletypes. The ESC key allows a key sequence to be entered in a
program, without that sequence being executed as a function.
ESC is always pressed and released prior to the entry of the key
sequence whose effect is to be negated. This entry of ESC
followed by the key sequence is known as an escape sequence.
For example, the following escape sequence,
ESCCtrl<
would cause the display not to be cleared when Ctrl< is
entered.
Other Atari Keys
The remaining Atari keys are used like those on a standard
typewriter.
Auto Repeat
Atari's auto repeat feature functions with every key except Shift,
Break, and System Reset. Auto repeat means that when a key is
continously pressed, that character will be repeated. For
example, if the A key is pressed, a single A will be displayed on
the screen. After a few seconds, the A will be repeated on the
display as long as the A key is depressed.
Display Line Length
The Atari's display width is 40 characters. As mentioned earlier,
the leftmost 2 characters comprise the left margin. Therefore,
only 38 character positions are usable per display line.
CHAPTER 3.
INTRODUCTION TO ATARI BASIC
Introduction
BASIC is probably the most widely used language in
microcomputers, with the Atari being no exception. Atari BASIC
is available in the ROM cartridge labeled "BASIC Computing
Language".
To use Atari BASIC, you must have the Atari BASIC ROM
cartridge. Also, you must have followed the correct start-up
procedure as outlined in Chapter 2. The READY message will be
displayed on the video screen when the Atari is ready to accept
BASIC commands.
Immediate & Program Modes
The immediate mode is also known as the direct or the calculator
mode. In the immediate mode, any BASIC command entry
results in the instructions being executed without delay. For
example, if the following immediate mode line was entered,
PRINT "Jim Smith"
the following would be displayed on the video screen.
Jim Smith
In the program or indirect mode, the computer accepts
program lines into memory, where they are stored for later
execution. This stored program is executed when the
appropriate command (generally RUN) is entered.
38 User's Handbook to the Atari 400/800 Computers
Illustration 3-1 contains an example of the entry of a program in
the program mode and its execution.
Illustration 3-1. Program Mode Entry & Execution
READY
NEW
READY
10 PRINT "Jim Smith"
20 PRINT "1220 Euclid Ave"
30 PRINT "Cleveland, OH 44122"
40 END
RUN
Jim Smith
1220 Euclid Ave
Cleveland, OH 44122
READY
Line Numbers
In the program mode, program lines must begin with a line
number. A line number is a one through five digit number
entered at the beginning of a program line. The line number at
the beginning of a program line is the only difference between it
and an immediate mode line.
Introduction to Atari BASIC 39
No two line numbers can be the same. If the same line number is
used more than once in a program, the line most recently
entered will replace the original. Line numbers can range from
to 32767.
The execution sequence of a BASIC program is determined by
the value of its line number. The lowest line numbers will be
executed first, followed by program lines with higher line
numbers. Even if program lines are not arranged in sequential
order, the Atari interpreter will place the lines in the correct
order.
Adding program lines to a program stored in the Atari's RAM is
very easy. Just type in the line number followed by the program
line. The line will be inserted in the program in the position
indicated by its line number. For example, by adding the
following line,
35 PRINT "216-777-5579"
to the program in Illustration 3-1, the phone number for Jim
Smith will be displayed on the line following his city, state, and
zip.
Program lines can be deleted by typing the line number to be
deleted followed by Return. For example, the following entry,
30 j
would result in line 30 being deleted.
Program lines can be changed by merely retyping the new line.
The existing line in the Atari's memory will be replaced with the
new line. For example, the following entry,
10 PRINT "Thomas Hill"
would result in "Thomas Hill" being output rather than "Jim
Smith" in the program in Illustration 3-1.
Program lines also can be changed by displaying them on the
40 User's Handbook to the Atari 400/800 Computers
screen with the LIST statement. Once that line has been listed to
the screen, it can be edited using the cursor control keys as
described in Chapter 2.
Once the desired changes have been made, these must be made
permanent. This is accomplished by pressing the Return key
while the cursor is within that line. Unless the Return key is
pressed somewhere within the line being edited, any changes
made effect only the video display. The cursor can be positioned
anywhere within the program line when Return is pressed.
NEW Command
You may have noticed the execution of the NEW command in
Illustration 3-1. The NEW command is used to erase an old
program from memory before a new one is typed in.
The Atari can only store one program in RAM at any one time. If
you attempt to enter a new program while another program is
already stored in RAM, the new program will be merged with the
existing program.
END Statement
Notice the last line in the program in Illustration 3-1. That line
consists only of the line number plus the BASIC reserved word
END.
The END statement identifies theend of a program, and instructs
Atari BASIC to return to the immediate mode. Obviously, the
END statement should be the last line in your program.
Actually, Atari BASIC does not require an END statement. When
the program's final statement isexecuted, it will end. However, it
is good programming practice to end a BASIC program with the
END statement.
Executing a Program
A program is executed in the program mode by entering the
RUN command. This is shown in Illustration 3-1. Every time RUN
Introduction to Atari BASIC 41
is executed, the program is re-executed. As previously
discussed, in the immediate mode, each program line is
executed when the Return key is pressed.
Program Lines & Display Lines
A display line can be defined as one row on the video display. A
program line is regarded by the BASIC interpreter as one line,
regardless of the number of display lines it occupies on the
screen. The end of a program line is signaled when the Return
key is pressed.
Program lines generally are limited to 114 characters. If you are
entering a lengthy program line, the Atari will beep when the
107th character has been input. This is intended as a warning to
the operator that he is approaching the limit of the program line.
Multiple Statement Program Lines
A statement can be defined as an instruction to the computer.
The terms statement and command are often used interchange-
ably. Most programs consist of a large number of statements. The
following are examples of statements.
PRINT "Tim Gregory"
070 DIM A(15)
100 C = 2*B
Every statement in Atari BASIC must contain at least one key or
reserved word. A keyword identifies the calculation, decision,
input, or output function to be performed. The keywords are
described individually in Chapter 5 and are listed in alphabetical
order in Appendix B.
In addition to keywords, numeric constants, string constants,
variables, and special symbols may appear in a BASIC statement.
These are known as the statement parameters.
Atari BASIC allows the user to place more than one statement on
a single program line. Multiple statements must be separated
with a colon (:). The following is an example of a multiple
42 User's Handbook to the Atari 400/800 Computers
statement program line.
100 A = B * 7:PRINT A:PRINT B
Abbreviating Keywords
Many of the Atari BASIC keywords can be abbreviated. For
example, the keyword PRINT can be abbreviated with the
symbol "?". Generally however, keywords are abbreviated with a
single letter or several letters followed by a period. Forexample,
the keyword GOTO can be abbreviated as follows.
G.
The various abbreviations for the keywords are contained in
Appendix B.
Listing a Program
As mentioned earlier, the LIST command can be used to display
program lines currently stored in RAM. Remember, if the NEW
command is issued or if the Atari is turned off, the program in
RAM will have been erased, and can no longer be displayed by
LIST.
LIST is used with the following configuration,
LIST {line 1, line 2)*
where line 7 is the line number of the first line to be listed, and
line 2 is the line number of the last line to be listed.
LIST can be used without any parameters to list the entire
program. LIST can also be used with a single line number to list
just that program line.
*ln this chapter, a standard format will be used to describe BASIC
keyword configurations. The keyword will be displayed in our
regular type style in upper case. Parameters will be displayed in
our italic type style in lower case. Optional parameters will be
enclosed in parentheses.
Introduction to Atari BASIC 43
Error Messages
When the Atari encounters a statement with an error, an error
message will be displayed. The error message consists of the
following.
ERROR- message
message can be the statement causing theerrorora diagnostic
error message number. These error numbers are
listed in Appendix A.
BASIC Data Types
Data can be classified under two major categories: text and
numeric. Text data consists of characters. These characters are
generally used within strings.
Examples of numeric data include:
Integers
Floating Point Numbers
Scientific Notation
Each of these data types will be discussed in the following
sections.
Strings
A string consists of one or more characters enclosed within
double quotation marks. The following are examples of strings:
"F. Scott Fitzgerald"
"149 Lexington Ave"
"New York, NY 10017"
"212-349-9879"
Notice that a string can contain both letters, numbers, and
symbols. Any string containing numbers can not be used in a
mathematical operation, unless it is first converted into numeric
data. String to numeric data conversion is covered in Chapter 4.
44 User's Handbook to the Atari 400/800 Computers
Numeric Data
Atari BASIC stores all numbers in memory in floating decimal
point form. With floating decimal point numbers, a decimal
point is always assumed. Any number of digits can be placed on
either side of this decimal point. Even with numbers with no
decimal position, a decimal point always is assumed following
the number's last digit.
Commas may not be included within numeric data. For example,
109000 would be a valid number in Atari BASIC, while 109,000
would be invalid.
Integer
An integer is a number without a decimal position. Integers can
either be positive or negative. The following are examples of
integers:
-1134
1
-1
17945
+32
Negative integers are preceded with the (-) sign. Positive
integers can be preceded with the (+) sign, although integers
without a (+) sign are assumed to be positive.
In Atari BASIC, integers are processed exactly as are any other
floating point numbers. Atari BASIC does not process integers as
a separate form of numeric data.
Floating Point Numbers
Floating point numbers include both integers, as well as decimal
functions and numbers with decimal positions. The following
are examples of floating point numbers.
Introduction to Atari BASIC 45
-.0789
5
77.39
+.000001
67.98
Again, negative floating point numbers should be preceded with
the minus sign (-). Positive floating numbers can optionally be
preceded with the plus sign (+), however, a floating point
number is assumed positive if it doesn't have a sign.
Scientific Notation
Atari BASIC uses scientific notation to express either extremely
large or extremely small numbers. A number in scientific
notation takes the following format:
± x E yy
Where;
± is an optional plus or minus sign.
x can either be an integer or a floating point number. This
position of the number is known as the coefficient or
mantissa.
E stands for exponent
yy is a one or two digit exponent. The exponent gives the
number of places that the decimal point must be moved to
give its true location. The decimal point is moved to the
right with positive exponents. The decimal point is moved
to the left with negative exponents.
The following examples specify a number in both standard
floating point and scientific notation:
1000000
— ^1 E6
.000001
— »-1 E-6
57500000
— *~5.75 E+07
00000479-
—^4.79 E-
-06
46 User's Handbook to the Atari 400/800 Computers
Any numbers containing more than 10 digits will beexpressed in
scientific notation. Also, any decimal number which contains
more than two digits to the right of the decimal point will be
expressed in scientific notation.
Atari BASIC can only handle floating point numbers expressed in
scientific notation in the range between -9.99999999 E+97 and -
9.99999999 E+97. Any decimal numbers that are closer to zero
than +9.99999999 E-98 or -9.99999999 E-98 will be converted to 0.
Rounding
In Atari BASIC, floating point numbers can have at most 9
significant digits. Any digits beyond 9 are replaced with zeros,
beginning with the least significant digit.
The following examples give the values used by Atari BASIC for
floating point numbers containing more than 9 digits.
17898743214798— ► 1.78987432 E+13
-879836341832—^8.79836341 E+11
7005.32144587931 — *■ 7005.32144
Fractional numbers in the range between 1 and -1 also may
contain a maximum of nine digits. However, with numbers in
this range, the nine significant digits are counted beginning with
the first non-zero digit to the right of the decimal point.
The following examples give the values used by Atari BASIC for
floating point numbers in the range between 1 and -1 which
contain more than 9 digits.
.87547983621— *- 0.874579836
.1 27894789874321 87—*- 0.1 27894789
-.478947821 765789— *- 0.478947821
.000000001407936579463 — ** 1 .40793657 E-09
Introduction to Atari BASIC 47
BASIC Variables
So far, we have only discussed data constants. A constant can be
defined as a fixed value. The following are examples of string and
numeric constants.
"Jack Novet"
"375"
27.59
100000
A name can be used to express data as well as a constant.
Variables are used to express data as a name.
A variable can be defined as a quantity that can assume any one
of a group of values. Variables are represented by variable
names. These consist of a letter followed optionally by additional
letters and/or numbers. The value assumed by a variable is
subject to change, depending upon the program statement
being executed. For example, in the following,
100 LET A = 5.0
200 LET B = 7.0
300 LET A = A + B
the variable A is initially assigned a value of 5.0 and Bis assigned a
value of 7.0. In line 300, the variable A is assigned a new value
equal to the sum of variables A and B, which is 12.0. The previous
value of A is erased.
Note the use of the LET statement in the preceding example. The
LET statement is used to assign a value to a variable. Whenever a
LET statement is used in a program, the value of the variable on
the left side of the equation is to be replaced with the value
appearing on the right.
The reserved word, LET need not actually be included in a LET
statement. Both of the following statements have the same
48 User's Handbook to the Atari 400/800 Computers
meaning.
100 LET A = 5
200 A = 5
BASIC Variable Names
Atari Basic allows any group of up to 114 characters to be used as
a variable name— as long as the first character of the group is a
capital letter of the alphabet, and as long as the variable name
does not duplicate a reserved word (see Appendix B). Examples
of reserved words are:
LET, GOTO, IF, READ, DATA
The following are examples of valid BASIC variable names,
A
JOHN
B23456
N4N
TOTAL.DATA
B%
A2
N
while the following are invalid variable names:
2BB7
END
1A
FOR
PRINT
COS
All of the preceding examples of valid variable names should be
used to represent numeric data. Variable names can also be used
to represent string data. These are known as string variables.
String variable names consist of a valid variable name followed
by the dollar sign ($). The following are examples of valid string
variable names.
A$
B1P$
A7$
Introduction to Atari BASIC 49
Before a string variable can be used in a program, it must first be
dimensioned with the DIM statement. If a string variable is not
dimensioned before it is used in a program, the error 9 will occur.
A string variable is dimensioned by giving its name and its
maximum size after the reserved word DIM. The maximum size
must be enclosed in parentheses. The following DIM statement,
100 DIM A$(5)
dimensions a five character string. More than one string variable
can be dimensioned in a single DIM statement. For example, the
following DIM statement,
100 DIM A$(10), B$(5), C$(7)
would dimension 3 string variables.
Tables & Arrays
Earlier in this chapter, we introduced the concept of variables. A
variable is designed to hold a single data item— either string or
numeric. However, some programs require that hundreds or
even thousands of variable names be used.
Obviously, the use of thousands of individual variable names
could prove extremely cumbersome. To overcome this
problem, BASIC allows the use of subscripted variables.
Subscripted variables are identified with a subscript, a number
appearing within parentheses immediately after the variable
name. An example of a group of subscripted variables is given
below:
A(0), A(1), A(2), A(3), A(4),..., A(100)
Note that each subscripted variable isa unique variable. In other
words, A(0) differs from A(1), A(2), A(3), A(4), etc.
Subscripted variables should be visualized as an array (or table).
In our previous example, the data contained in the array defined
by A would consist of one row with 101 columns in it. Such an
array is a single-dimension array.
50 User's Handbook to the Atari 400/800 Computers
An array can also consist of two dimensions. Such an array is
known as a two-dimensional array (or table). An example of an
array of 4 rows and 3 columns is shown in Illustration 3-2.
A two-dimensional array contains two subscripts. The first
subscript contains the row location, while the second subscript
contains the column location. The subscripted variable A(1,0)
identifies the darkened area in the array shown in Illustration 3-
2.
Illustration 3-2. Two-Dimensional Array
Columns
Rows
1 2
In the Atari BASIC, arrays can be used to represent numeric data.
String arrays cannot be used in Atari BASIC.
Before any array variable can be used in a program, the size of
that array must have been defined so that BASIC can reserve a
memory area for it. This is also accomplished with the DIM
statement. A single dimension numeric array with 11 variables
could be defined with the following DIM statement:
DIM A(10)
Remember that array subscripts begin with 0. Therefore, the
numeric array A which was dimensioned in the preceding
statement, would have space reserved for the 11 array elements,
not 10.
Introduction to Atari BASIC 51
More than one array can be defined with a single DIM
statement. This is shown in the example below:
TOO DIM Z(5,2), B(100), C(2,3)
A DIM statement must appear in a program before the array
variable it is dimensioning appears. If an array variable is used in
a program before it is dimensioned, error 9 will occur.
Expressions and Operators
The values of variables and constants are combined to form a
new value through the use of expressions. The following are
examples of expressions.
4 + 7
A$+ B$
3 A 2
14 < 21
X AND Y
Atari BASIC includes several types of expressions including
arithmetic, relational, and Boolean. In our previous examples,
the first three examples are arithmetic expressions, while the
fourth and fifth are examples of relational and Boolean
expressions respectively. Each of these types of expressions will
be discussed in detail in the following sections.
The sign or phrase describing the operation to be undertaken is
known as the operator. The operators in our previous example
were as follows:
+
+
A
AND
The constants or variables which are affected by the operator are
known as operands.
52 User's Handbook to the Atari 400/800 Computers
Compound Expressions and Order of Evaluation
All of our preceding examples were simple expressions. A simple
expression is one which contains just one operator and one or
two operands. Simple expressions can be combined to form
compound expressions. The following are examples of
compound expressions.
(A + B) * 7- 4
(A + B) AND (C +D)
IF A = 1 AND B = 1 THEN C = 1
With compound expressions, it is necessary that the computer
knows which operation should be undertaken first. Atari BASIC
follows a standard order or evaluation within compound
expressions. This order is outlined in Table 3-1.
Note that parentheses have the highest precedence level. In
other words, any expression enclosed within parentheses will be
evaluated first. If more than one set of parentheses appears in an
expression, these will be evaluated from left to right.
One pair of parentheses can be used to enclose an operator
enclosed within another set. In such an instance, Atari BASIC will
evaluate the expression within the innermost set of parentheses
first, followed by the next innermost set, etc.
When expressions have the same order of evaluation, they will
be evaluated in order from left to right within the compound
expression.
Introduction to Atari BASIC 53
Table 3-1. Order of Evaluation
Operator
Description
Parentheses
( )
Used to alter order
of evaluation.
A
Exponentiation
-
Unary Minus
Arithmetic
*
Multiplication
Operators
/
Division
+
Addition
-
Subtraction
=
Equal To
< >
Not Equal To
Relational
<
Less Than
Operators
>
Greater Than
< =
Less Than or Equal To
> =
Greater Than or Equal To
Boolean
NOT
Logical Complement
Operators
AND
Logical AND
OR
Logical OR
Arithmetic Operations
The symbols used for addition, subtraction, multiplication,
division, and exponentiation are known as arithmetic operators
in BASIC. The symbols + and - are used for addition and
subtraction respectively. The asterik (*) is used to indicate
multiplication, while the slash (/) is used to indicate division.
When a + or - sign precedes a number, the symbol is used to
specify that number's sign. When + or - is used to change a
54 User's Handbook to the Atari 400/800 Computers
number's sign, that usage is known as a unary operation. Unary
operators can be used to change the sign of a numeric constant
or variable as shown below:
100 LET A =-A
When unary operators are used in the manner shown above, the
unary operation is regarded as an arithmetic operation.
The term arithmetic expression is used to describe the use of an
arithmetic operator with numeric constants and/or variables.
The following are examples of arithmetic expressions.
X + Y + 70
100/ A + B
3000 * 10 + 1
Exponentiation is the process of raising a number to a specified
power. For example, in the following,
A 5
the numeric variable A would be evaluated as:
A*A*A*A*A
In BASIC, exponentiation is indicated with the caret symbol, A .
Exponentiation can be used inanarithmeticexpressionasshown
below:
8*3+7 A 2
The preceding expression would evaluate to 73.
Introduction to Atari BASIC 55
Relational Operators
The following relational operators are used in Atari BASIC.
<
< »- less than
*- less than or equal to
> *- greater than
3 -= *~ greater than orequal to
*~ equal to
*- not equal
A relational operation evaluates to either true or false. For
example, if the constant 1.0 was compared to the constant 2.0 to
see whether they were equal, the expression would evaluate to
false. In Atari BASIC, a value of 1 represents a condition of true,
while a value of represents false.
The only values returned by a comparison in BASIC are 1 (true)
or (false). These values can be used as any other integer would
be used. The following results are generated by the following
relational expressions.
5>7—*~0 (false)
3 = 3— «-1 (true)
2<>2-*0 (false)
(2 = 2) * 4 — 4
(1>7)+7 — 7
The first three examples are easy enough to understand. In the
fourth example, the relational expression (2=2) is evaluated first
as true or 1. This result is then multiplied by 4 with a product of 4
as the result. In the fifth example, the relational expression (1 >
7) evaluates as false or 0. This result is added to 7, with the result
being 7.
Relational operations using numeric operations are fairly
straightforward. However, relational operations using string
values may prove confusing to the first-time computer user.
56 User's Handbook to the Atari 400/800 Computers
Strings are compared by taking the ASCII value for each
character in the string one at a time and comparing the codes.
If the strings are of the same length, then the string containing
the first character with a lower code number is the lesser. If the
length of the strings are unequal, then the shorter string is the
lesser. Blank spaces are counted and have an ASCII value of 32.
The following comparisons between strings would all evaluate as
true.
"ABC"="ABC"
"ABC "=> "ABC"
"aAA" >"AAA"
"Alfred" < "Zachary"
A$ < Z$ where A$ = "Alfred" and Z$ =
"Zachary"
Note that all string constants must be enclosed in quotation
marks when used as constants.
Logical Operators
Logical or Boolean operations are generally used in Atari BASIC
to compare the outcomes of two relational operations. Logical
operations themselves return a true or false value which will be
used to determine program flow.
The logical operators are NOT (logical complement), AND
(conjunction), and OR (disjunction). These are best explained
with a simple analogy. Suppose that Steve and Sherry were
shopping in the produce department of their grocery store. If
they decided to collectively purchase an item if either of them
individually wanted that item, they would be acting under the
OR logical operator.
Now, suppose that Steve and Sherry decided that they would
only purchase an item if they both wanted that item. They would
then be acting under the AND logical operation.
Now, suppose that Sherry was angry with Steve. If Sherry
Introduction to Atari BASIC 57
decided not to purchase the items that Steve wanted, she would
be acting under the NOT logical operation. The NOT, AND, and
OR logical operators are summarized in Illustration 3-3.
A logical operator evaluates an input of one or more operands
with true or false values. The logical operator evaluates these
true or false values and returns a value of true or false itself. An
operand of a logical operator is evaluated as true if it has a non-
zero value. (Remember, relational operators return a value of 1
for a true value.). An operand of a logical operator isevaluated as
false if it is equal to zero.
The result of a logical operation is also a number, which if non-
zero is considered true, and false if it is zero.
The following are examples of the use of logical operators in
combination with relational operators in decision making.
IF X >10OR Y < OTHEN 900
IF A > AND B > THEN 200 ELSE GOTO 300
B = -1:PRINT NOT B
In the first example, the result of the logical operation will be
true if variable X has a value greater than 10 or if variable Y has a
value less than 0. Otherwise, it will be false. If the result of the
logical operation is true, the program will branch to line 900.
Otherwise, it will continue to the next statement.
In the second example, the result of the logical operation will be
true only if the value of both variables A and B are greater than
zero. If the result of the logical operation is true, program
control will branch to line 200. Otherwise, program control will
branch to line 300.
In the third example, B is set to a value of -1 (true). The value of
NOT B is then printed. This will be or false.
Illustration 3-3 contains tables that may prove of help when
evaluating program statements using logical operators in
combination with relational operators.
58 User's Handbook to the Atari 400/800 Computers
Illustration 3-3. Logical Operators
NOT Operation
T
F
F
T
A Operand
NOT A
AND Operation
T
T
F
F
T
F
T
F
T
F
F
F
A Operand
B Operand
A AND B
OR Operator
T
T
F
F
T
F
T
F
T
T
T
F
A Operand
B Operand
A OR B
Introduction to Atari BASIC 59
Atari BASIC Statements
In the next several sections, we will discuss many of the more
commonly used statements in Atari BASIC. These include the
following:
Remark Statements
Assignment Statements
Output Statements
Input Statements
Loops
Conditional Statements
Branching Statements
Subroutines
STOP, END Statements
Atari BASIC Functions
Remark Statements
Remark statements are used to include a programmer's
comments within a program. It is good programming practice to
include numerous Remark statements in your programs. Not
only do Remark statements make your programs easier for
others to understand, they also help you remember your
program's logic.
Remark statements consist of a line number, the reserved word
REM, and the programmer's comment. An exampleof a Remark
statement is given below.
100 REM Initialize I to
Remark statements are ignored by the Atari BASIC interpreter,
but are included in program listings.
60 User's Handbook to the Atari 400/800 Computers
In multiple line statements, the REM statement must be the final
statement. The Atari BASIC interpreter ignores all text following
the keyword REM.
REM can be abbreviated as R. or with the period (.).
Assignment Statements
Assignment statements were discussed briefly earlier in this
chapter. Assignment statements are used to assign values to
variables. The following are examples of assignment statements.
100 LET A = 7
200 B = 42
300 NAME$ = "Phil"
400 X=1:Y=2:Z=3
Notice that the keyword LET is optional. Generally, LET is
assumed. Both string and numeric variables can be assigned
values with an assignment statement. Also, multiple assignment
statements can be included in a single line, aslongaseach of the
individual statements is separated by a colon.
DATA, READ Assignment Statements
Assigning values to a large number of variables with individual
assignment statements could prove very cumbersome. The
DATA, READ statements can be used to assign values to a large
number of variables. The following is an example of a DATA,
READ statement.
100 DATA 100, 500, 1000, "Jack"
200 READ A, B, C, D$
The DATA statement creates a list of constant values known as a
DATA list.The items in the DATA list are assigned sequentially to
the variables in the READ statement. A DATA list is depicted in
Illustration 3-4.
Introduction to Atari BASIC 61
Illustration 3-4. DATA List
100 DATA 100, 200, 300, 400, 500
400 DATA Monday, Tuesday, Wednesday,
Thursday, Friday
500 READ A, B, C, D, E
600 RESTORE
700 READ F, G, H, I, J-
900 READ A$, B$, C$, D$, E$
400,600 — *-DATA list pointer
position after the execution of lines
400 and 600.
500,700 — "-DATA list pointer
position after the execution of lines
500 and 700.
900 — "-DATA list pointer position
after execution of line 900.
400,600-
A J
B G
C H
D
I
B$
C$
D$
E$
900-
DATA List
100
200
300
400
500
Monday
Tuesday
Wednesday
Thursday
Friday
DATA statements may contain numeric or string values. These
values must be separated or delimited with commas. DATA
statements may appear at any point in the program. No other
statements can appear in the same program line with a DATA
statement.
The DATA list uses a pointer to indicate which value within the
list is to be assigned to the next variable in a READ statement.
Before the first READ statement is encountered, the DATA list
62 User's Handbook to the Atari 400/800 Computers
pointer will point at the first value in the DATA list. As values
from the DATA list are assigned to variables in the READ
statement, the pointer will move sequentially to each successive
item in the DATA list.
The values from the DATA list must match the type of variable to
which they are assigned in the READ statement. In other words, a
string value can not be assigned to a numeric or vice versa.
The RESTORE statement is used to reset the DATA list. In
Illustration 3-4, note the use of the RESTORE statement. After
DATA list values have been read into A, B, C, D, and E in line 500,
a RESTORE statement is executed. This causes the DATA list
pointer to be reset to the beginning of the DATA list.
Outputting Data
In some of our preceding examples, we touched upon the use of
the PRINT statement to display data. The PRINT statement can be
used to display both numeric and string data.
The following program statement,
100 PRINT "Vendor List"
would display the following at the current cursor position.
Vendor List
The first item in a PRINT statement is displayed at the cursor's
current location.
Several strings can be displayed on the same line with a single
PRINT statement by separating the string constants or variables
in the PRINT statement with commas. The following statements,
050 DIM A$(10)
100 LET A$ = "John"
200 PRINT A$, "Bill", "Peter"
Introduction to Atari BASIC 63
would result in the display shown below:
John Bill Peter
Atari BASIC divides the spacing on a line into a series of print
zones. Each print zone contains 10 spaces. When a comma
appears in a PRINT statement, the computer is instructed to
begin printing the next parameter in the PRINT statement at the
beginning of the next print zone. In our example above, John
would begin in column 1 (print zone 1); Bill in column 11 (print
zone 2); and Peter in column 21 (print zone 3).
A semicolon can also be used to separate the items in a PRINT
statement. A semicolon causes the next item in the PRINT
statement to be displayed immediately after the preceding item.
Unlike the use of the commas in a PRINT statement, when
semicolons are used to separate items, no blank spaces appear
between the items when they are displayed.
When a PRINT statement has finished execution, the cursor
moves to the left margin of the following line. This is known as a
carriage return/line feed.
If a comma or semicolon occurs at the end of a PR I NT statement,
the carriage return/line feed will be suppressed. If a comma is
placed at the end of the PRINT statement, the next PRINT
statement will begin output at the next print zone after the last
item is displayed. If a semicolon is placed at theend of the PRINT
statement, the next PRINT statement will begin output
immediately following the last item displayed.
In this section, we have only discussed sending output to the
video display. Output can also be sent to the printer. This is
accomplished by using the LPRINT statement in place of PRINT.
The LPRINT statement is used exactly as the PRINT statement in
Atari BASIC.
However, the LPRINT statement does have some variations
when it is used with the Atari 825 Printer. These variations occur
when a comma or semicolon is used to end the PR I NT statement.
If an LPRINT statement is used to print more than 40 characters,
64 User's Handbook to the Atari 400/800 Computers
any subsequent LPRINT statements will be started on a new line
on the Atari 825.
However, if an LPRINT statement prints 38 characters or less and
ends with a comma, output from any subsequent LPRINT
statement will be begun on the same line at print position 41.
Printing also begins at this position, if LPRINT is used to print 40
characters or less and ends with a semicolon.
INPUT Statements
Data can be input into the computer while a program is being
executed. This is accomplished with the INPUT statement. For
example, when the following statement is executed,
100 INPUT A
the computer will display a question mark and wait for the
operator to enter a response. That entry will be assigned to the
variable A. The entry must be ended by pressing the Enter key.
Program execution will then resume.
The values of several numeric variables can be input with a single
INPUT statement as shown in the example below.
200 INPUT X, Y, Z
When the preceding INPUT statement is executed, the INPUT
prompt (?) will be displayed. The operatorshould then enterthe
data items for X, Y, and Z. Each input should be separated by a
comma. The Return key should be pressed after all input entries
have been made. An example of a valid entry for the preceding
INPUT statement is given below.
100, 200, 300 /
The INPUT statement in Atari BASIC functions somewhat
differently with string inputs than with numeric inputs.
First of all, the string variable used with INPUT must have been
dimensioned earlier in the program.
Introduction to Atari BASIC 65
Secondly, the number of characters entered in response to tPie
INPUT prompt cannot exceed the number of characters that the
string variable specified in INPUT was dimensioned for. For
example, in the following,
100 DIM A$(5)
200 INPUT A$
the string variable A$ is only dimensioned for 5 characters in line
100. If the operator attempts to enter a string greater than 5
characters in response to the INPUT prompt in line 200, Atari
BASIC will ignore any additional characters.
Finally, if string variables are included as one of a number of
variables in an INPUT statement, the value for each string
variable must be entered on a separate line. In the following
INPUT statement,
500 INPUT A, B, C$, D$
the operator might respond to the INPUT prompt as follows:
100, 200, JOHN /
MARY >
The reason for the entry of string data on separate lines is that
Atari BASIC allows a comma to be input as part of a string.
Therefore, the comma cannot be used as a delimiter. You can
test this by entering the following,
SMITH, JOHN /
for one of the string variables in our preceding example.
It is good programming practice to include a prompt message in
conjunction with an INPUT statement to let the operator know
what data the computer is expecting. This is accomplished by
preceding the INPUT statement with a PRINT statement. If the
PRINT statement is ended with a semicolon, the prompt message
will be displayed on the same line with the INPUT prompt.
66 User's Handbook to the Atari 400/800 Computers
100 PRINT "ENTER YOUR AGE";
200 INPUT AGE
In the preceding example, the prompt, "ENTER YOUR AGE", will
appear on the same line as the INPUT prompt.
Loops
Suppose that you needed to compute the squares of the integers
from 1 to 20. One way of doing this is by calculating the square
for each individual integer as shown below.
100 A = 1 A 2
200 PRINT A
300 B = 2 A 2
400 PRINT B
500 C = 3 A 2
600 PRINT C
However, this method is very cumbersome. This problem
could be solved much more efficiently through the use of a
FOR, NEXT loop as shown below.
100 FOR A =1 TO 20
200 X = A A 2
300 PRINT X
400 NEXT A
500 END
The sequence of statements from 100 to 400 is known as a loop.
When the computer encounters the FOR statement in line 100,
the variable A is set to 1. X is then calculated and displayed in
lines 200 and 300.
The NEXT statement in line 400 will request the next value for A.
Execution returns to line 100 where the value of A is incremented
by 1 (to 2) and then compared to the value appearing after TO.
Since the value of A is less than that value, the loop will be
executed again with the value of A set at 2.
Introduction to Atari BASIC 67
The loop will continue to be executed until A attains a value
greater than 20. When this occurs, the statement following the
NEXT statement will be executed.
In our preceding example, A is known as an index variable. If the
optional keyword STEP is not included with the FOR statement,
the index variable will be incremented by 1 every time the NEXT
statement is executed.
STEP can be included at the end of a FOR statement to change
the value by which the index variable is incremented. The
integer appearing after STEP is the new increment. For example,
if our preceding example were changed as follows,
100 FOR A = 1 TO 20 STEP 2
200 X = A A 2
300 PRINT X
400 NEXT A
500 END
the index variable A would be incremented by 2 every time the
NEXT statement was executed.
Nested Loops
One loop can be placed inside of another loop. The innermost
loop is known as a nested loop. The following program contains
a nested loop.
100 P = 1000
200 FOR Y = 1 TO 10
300 FOR Q = 1 TO 4
400 P = P + P * .02
500 NEXT Q
600 NEXT Y
650 PRINT P
700 END
Our preceding example is used to calculate the value of 1000
after 10 years with an interest rate of 8% compounded quarterly.
One error that you should take care to avoid when using nested
68 User's Handbook to the Atari 400/800 Computers
loops is to end an outer loop before an inner loop is ended. Also,
be certain that that every NEXT statement has a matching FOR
statement. If the Atari BASIC interpreter cannot match every
NEXT statement with a preceding FOR statement, an error will
result.
Conditional Statements
One of the most important features of a computer is its ability to
make a decision. BASIC uses the IF, THEN, ELSE statement to take
advantage of the computer's decision making ability. The IF,
THEN, ELSE statement takes the following form:
IF expression THEN statement ELSE statement
The IF statement sets up a question or a condition. If the answer
to that question is true, the statement following THEN is
executed. If the answer is false, thestatement following ELSE will
be executed.
In the following example, if X is equal to 0, then Y will be set to 1.
If X is not equal to 0, Y will be set to 0.
100 IF X = THEN Y = 1 ELSE Y =
The IF, THEN, ELSE statement may be shortened to just IF, THEN
as shown below.
050 Y =
100 IF X = 1 THEN Y = 1
In this example, if X is equal to 1, the statement following THEN
will be executed. If X is not equal to 1, program execution will
continue with the next program statement (in ourexample— line
200).
Branching Statements
Branching statements change the execution pattern of programs
from their usual line by line execution in ascending line number
order. A branching statement allows program control to be
Introduction to Atari BASIC 69
altered to any line number desired. The most commonly used
branching statements in BASIC are GOTO and GOSUB.
GOTO takes the following format:
GOTO line number
For example, the following program statement:
500 GOTO 999
999 END
would branch program control at line 500 to line 999.
Branching statements are often used in conjunction with
conditional statements. In such a situation, the normal execution
of the program is altered depending upon the outcome of the
condition set up in the IF statement. This is shown in the
following example.
050 DIM A$(99)
100 PRINT "ENTER THE AMOUNT"
150 INPUT A
200 IF A = THEN GOTO 900
900 PRINT "ARE YOU FINISHED (Y/N)": INPUT A$
910 IF A$ = "N" THEN 100
999 END
In our preceding example, if the value input for A has a zero
value, then the program will branch to line 900 where the
operator will be prompted whether he has finished entering
data. In line 910, the program will set up a condition where if the
input was'N', the program will branch to line 100. If the entry was
not equal to 'N', the program will continue to line 999.
70 User's Handbook to the Atari 400/800 Computers
Note in line 910 that a GOTO statement is not used to precede
the line number being branched to. When a line number is
indicated following a THEN or ELSE statement, the computer
does not require the presence of GOTO, which is assumed.
ON, GOTO Statement
The ON, GOTO statement is a combination of a conditional
statement and a branching statement. The use of the ON, GOTO
statement is illustrated in the following program.
100 INPUT A
200 ON A GOTO 250,260
210 GOTO 999
250 PRINT A: GOTO 100
260 PRINT A A 2:GOTO100
999 END
If the variable or expression following ON evaluates to 1,
program control branches to the first line numberspecified after
GOTO; if 2, to the second; if 3, to the third, etc.
If the variable or expression evaluates to a number greater than
the number of line numbers following GOTO, program control
will branch to the statement immediately following the ON,
GOTO statement. This is also the case if the variable or
expression following ON evaluates to zero.
Subroutines & GOSUB Statements
Many times you will find that the same set of program
instructions are used more than once in a program. Re-entering
these instructions throughout the program can be very time
consuming. By using subroutines, these additional entries will be
unnecessary.
A subroutine can be defined as a program which appears within
another larger program. The subroutine may be executed as
many times as desired.
Introduction to Atari BASIC 71
The execution of subroutines is controlled by the GOSUB and
RETURN statements. The format for the GOSUB statement is as
follows.
GOSUB line number
The computer will begin execution of the subroutine beginning
at the line number indicated. Statements will continue to be
executed in order, until a RETURN statement is encountered.
Upon execution of the RETURN statement, the computer will
branch out of the subroutine back to the first line following the
original GOSUB statement. This is illustrated in the following
example.
Illustration 3-5. BASIC Program With a Subroutine
050 DIM ER$(50), B$(50)
100 PRINT "ENTER CHECK AMOUNT"
200 INPUT A
300 GOSUB 900
400 PRINT "ENTER PAYEE'S NAME"
500 INPUT B$
600 PRINT B$, A
700 GOTO 100
900 REM ERROR SUBROUTINE
910 ER$ = "NOT ALLOWED"
920 IF A < THEN GOTO 100
Subroutine < 930 IF A>1000 THEN PRINT ER$
940 IF A = THEN 999
950 RETURN
999 END
Subroutines can help the programmer organize his program
more efficiently. Subroutines also can make writing a program
easier. By dividing a lengthy program into a number of smaller
subroutines, the complexity of the program will be reduced.
Individual subroutines are smaller and therefore more easily
written. Subroutines are also more easily debugged than a
longer program.
72 User's Handbook to the Atari 400/800 Computers
ON, GOSUB Statement
The ON, GOSUB statement is very similar in nature to the ON,
GOTO statement. The following statement is an example of an
ON, GOSUB statement.
100 ON X GOSUB 1000, 2000, 3000
If the value of X is 1, the subroutine at line 1000 is executed. If X is
2, the subroutine at line 2000 is executed. If X is 3, the subroutine
at line 3000 is executed. If X evaluates toOor to a number greater
than 3, the statement immediately following the ON, GOSUB
statement will be executed.
If ON, GOSUB causes a branch to a subroutine, program control
will revert to the line immediately following the ON, GOSUB
statement, once the subroutine has been executed.
Break Key and CONT
Generally, Atari BASIC programs can be stopped by pressing the
Break key. When the Break key is used to stop program
execution, a message similar to the following will be displayed.
STOPPED AT LINE XXX
In actual practice, the XXX will be replaced by the line number
where program execution stopped.
Once program execution has been stopped by pressing the
Break key, the computer will return to the immediate mode. If
you wish program execution to resume, enter the CONT
command at the keyboard. Program control will resume with the
line following the one where the program break occurred.
System Reset Key
Program execution can also be stopped at any time by pressing
the System Reset key. However, System Reset functions
somewhat differently than Break.
Introduction to Atari BASIC 73
When System Reset is pressed, the program will stop executing,
the display screen will be erased, and the ATARI will return to
the immediate mode. You may be able to resume program
execution by entering CONT. However, this is not assured. With
complex programs, chances are slim that program execution can
be resumed once System Reset has been pressed.
STOP STATEMENT
The STOP statement functions in much the same manner as
pressing the Break key.Thefollowing isan exampleof a program
line containing a STOP statement.
500 STOP
When the statement is executed, program execution will be
halted, and the following message will be displayed.
STOPPED AT LINE 500
The program will return to the immediate mode, where
execution can be resumed by entering CONT.
END Statement
The END statement also causes program execution to halt. An
example of an END statement is given below.
999 END
When an END statement is executed, program execution will
halt, the message READY will be displayed on the screen, and the
computer will return to the immediate mode.
Execution can be resumed with the line following the END
statement by entering CONT.
Unlike the STOP statement, the END statement closes any open
input/output channels, sets the screen to graphics mode 0, and
turns off all sound voices.
74 User's Handbook to the Atari 400/800 Computers
When the Atari runs out of BASIC program statements, an END
statement is automatically executed.
Atari BASIC Functions
Functions are used in Atari BASIC to perform predefined
calculations or operations on their arguments. All functions use
the following format.
function (argument)
function is the keyword for the function, argument is a variable,
constant, or expression which is to be used in the operation
defined by the function.
The following statement is an example of the use of the SQR
function.
100 A =SQR(49)
In this example, A would evaluate at 7. SQR is the keyword which
describes the square root function. The square root of 49 is, of
course, equal to 7.
Functions can be used with arithmetic, relational, and Boolean
expressions, as shown in the following statement.
100 X = 100-7* SQR(49)
In an expression containing functions as well as arithmetic,
relational, and/or Boolean operators, the function's value is
calculated first. In our preceding example, the square root of 49
would be calculated, that value would be multiplied by 7, and
the product subtracted from 100.
The various Atari BASIC functions are described in Chapter 5.
CHAPTER 4.
ADVANCED ATARI BASIC
Introduction
In this chapter, we will expand on the concepts of BASIC
programming that were introduced in Chapter 3. The following
topics will be covered.
String Handling
Variable Storage
PEEK
POKE
Screen Output Programming
Input Programming
Prompt Messages
INPUT Response Checks
CHR$
ASC
TAB
Atari ASCII
The Atari can not store characters; it can only store numbers.
Before characters can be stored, they must be converted to
numbers. Computers use special numeric codes to store
characters. Most microcomputers use a code known as ASCII
(American Standard Code for Information Interchange).
The Atari uses a special version of ASCII known as Atari ASCII.
When we refer to ASCII in thisbook,wewill be referring to Atari
ASCII. The Atari ASCII code set is outlined in Appendix C.
76 User's Handbook to the Atari 400/800 Computers
String Handling
As a programmer, you will encounter a number of situations
where you may need to work with string data. For example, you
might want to combine several strings, compare two strings,
separate portions of a string, or even convert string data to its
numeric equivalent. Atari BASIC allows for all of these.
Substrings
Atari BASIC allows the programmer to extract a portion of a
string, known as a substring. However, Atari BASIC accomplishes
this extraction in a manner which is very different from other
versions of BASIC, which use MID$, RIGHTS, and LEFTS to
accomplish this task.
Atari BASIC uses the following configuration to extract a
substring.
NAMES (first, last)
Where NAMES is the name of the string from which thesubst ring
is to be extracted, first is the position of the first character from
NAMES to be included in the substring, and last is the position of
the last character from NAMES to be included in the substring.
For example, if X$ consisted of the following,
"JOHN JOHNSON"
the substring defined by X$ (1,4) would consist of "JOHN", and
X$ (6,12) would consist of "JOHNSON". Notice that the blank
space in X$ is counted as one character position.
The first and last character position in a substring specification
can be specified with a variable or an expression as well as a
constant. Also, the last character position need not be specified.
If it is not, the entire right hand portion of the string will be
returned beginning with the specified first character.
Substrings can be used to replace characters in larger strings. In
Advanced Atari BASIC 77
the following program, a substring is used to change X$ from
"JOHN JOHNSON" to "JOHN JACKSON".
100 DIM X$(15)
200 X$ = "JOHN JOHNSON"
300 X$(6,12) = "JACKSON"
400 PRINT X$
500 END
RUN
JOHN JACKSON
If an error occurs with a substring specification, error number 5
will be displayed.
String Concatenation
The process of joining together one or more strings is known as
concatenation. The LEN function is used in conjunction with
substrings in concatenation. The LEN function is used to return
the length of its string argument. LEN uses the following
configuration.
LEN (string)
The following program illustrates string concatenation in Atari
BASIC.
100 DIM X$(15), Y$ (15)
150 X$ = "":Y$ = ""
200 X$ = "JOHN"
300 Y$ = "JOHNSON"
400 X$(LEN(X$) + 1) = Y$
500 PRINT X$
600 END
RUN
JOHNJOHNSON
The actual concatenation takes place in line 400. Here, Y$ is
added onto the end of X$ to form a new X$. Notice that 1 was
added to the result of LEN(X$). This causes Y$ to be added
beginning at the first blank space following the end of the
original X$.
78 User's Handbook to the Atari 400/800 Computers
If line 200 was revised as follows,
200 X$ = "JOHN "
the following could be output:
JOHN JOHNSON
The addition of a blank space in X$ results in one additional
blank space being output.
CHR$ & ASC Functions
As mentioned earlier, characters are represented with the Atari
as ASCII codes. Atari BASIC'S CHR$ function can be used to
translate an ASCII code to its equivalent character. The following
short program illustrates the use of the CHR$ function.
100 PRINT CHR$ (54)
200 PRINT CHR$ (55)
300 END
RUN
6
7
The CHR$ function is often used to represent characters in a
statement, when that character can not be represented in its text
form. For example, in the following program,
100 PRINT CHR$(34); "JOHN JOHNSON"; CHR$(34)
200 END
RUN
"JOHN JOHNSON"
quotation marks are specified in the PR I NT statement using their
ASCII code and the CHR$ function.
The ASC function returns the ASCII code equivalent for its string
argument. If this string is longer than one character, the ASC
function returns the ASCII code for just the first character in the
string.
Advanced Atari BASIC 79
The following program illustrates the use of the ASC function:
050 DIM A$(20)
100 A$ = "JOHN JOHNSON"
200 PRINT ASC(A$)
300 END
RUN
74
Escape Sequences in Strings
Generally, the cursor movement characters may not be included
within a string. They may, however, be included if they are
preceded by the operator pressing the Escape key.
When the Escape key prefixes a cursor movement key, the
combination is known as an escape sequence.
The following program will illustrate the use of an escape
sequence.
100 PRINT "JOHN— N— JOHNSON"
200 END
RUN
JOHN JOHNSON
In our example, the symbol — denotes pressing ESC followed by
CTRL-+. The symbol — * denotes pressing ESC followed by
CTRL-*.
In our previous example, the cursor movement itself was
accomplished by using an escape sequence. Each cursor
movement is also associated with a character as shown in Table 4-
1. By pressing the Escape key twice before the cursor movement
key sequence, this character will be output. This is shown in the
following program.
100 PRINT " E Et E E t E Et "
200 END
RUN
tit
80 User's Handbook to the Atari 400/800 Computers
In this example, e e represents pressing the Escape key twice, and
| represents pressing Escape Ctrl—.
The various escape sequences are given in Table 4-1.
Table 4-1. Escape Sequences
ASCII
Echoed
Keyboard Entry
Code
Character
String Character
ESC/ESC
27
LH
Escape Code
ESC/CTRL-
28
m
Cursor Up
ESC/CTRL-=
29
m
Cursor Down
ESC/CTRL-*
30
a
Cursor Right
ESC/CTRL- +
31
B
Cursor Left
ESC/CTRL- <
125
m
Clear Screen
ESC/SHI FT- <
125
s
Clear Screen
ESC/BACK S
126
m
Cursor left, replace with
blank space
ESC/TAB
127
IB
Cursor right to next
tab stop
ESC/SHIFT-BACK S
156
n
Delete Line
ESC/SHI FT- >
157
D
Insert Line
ESC/CTRL-TAB
158
□
Clear Tab Stop
ESC/SHIFT-TAB
159
Q
Set Tab Stop
ESC/CTRL-2
253
□
Sound Built-in Speaker
ESC/CTRL-BACK S
254
□
Delete Character
ESC/CTRL->
255
D
Insert Character
Graphics Characters in Strings
The Atari has 29 graphic characters. These are output by using
the Control key in combination with another key. Table 4-2
contains a list of the graphics characters.
The graphics characters can be included in a string with a PRINT
statement to output graphics to the screen. For example, the
following program,
Advanced Atari BASIC 81
Table 4-2. Atari Graphics Characters
Decimal
ASCII
Decimal
ASCII
Code
Character
Keystrokes
Code
Character
Keystrokes
ffl
CTRL-,
15
E
CTRL-O
1
00
CTRL-A
16
a
CTRL-P
2
□
CTRL-B
17
a
CTRL-Q
3
E
CTRL-C
18
H
CTRL-R
4
E
CTRL-D
19
m
CTRL-S
5
B
CTRL-E
20
m
CTRL-T
6
CTRL-F
21
y
CTRL-U
7
H
CTRL-G
22
c
CTRL-V
8
a
CTRL-H
23
h
CTRL-W
9
a
CTRL-I
24
H
CTRL-X
10
E
CTRL-J
25
E
CTRL-Y
11
3
CTRL-K
26
H
CTRL-Z
12
E
CTRL-L
96
LH
CTRL-.
13
n
CTRL-M
123
LH
CTRL-;
14
u
CTRL-N
100 DIM A$(20)
200 A$ = "1- V -1"*
300 PRINT A$:PRlNT A$:PRINT A$
400 END
would result in a display similar to that shown in Illustration 4-1
when it is run.
V —is generated by pressing Ctrl-,
82 User's Handbook to the Atari 400/800 Computers
Illustration 4-1. Graphics Example Program Ouput
1- V --1
1-. y -1
1-V-1
Variable Storage
Atari BASIC keeps a list of the variable names used in a program
in its variable name table. A maximum of 128 variable names can
be stored in the variable name table. Therefore, an Atari BASIC
program is effectively limited to a maximum of 128 variables.
These include numeric, string, and array variables. An array
variable name counts as only 1 name in the variable name table,
regardless of the number of elements within that array.
Every time a new variable is entered in the immediate mode, that
name is added to the variable name table. In the program mode,
variables are added to the variable name table as they are
encountered in the program.
Advanced Atari BASIC 83
Variable names are stored in the variable name table until a NEW
command is issued. NEW causes the entire variable name table
to be cleared.
When a program is saved on cassette with the CSAVE statement,
the variable name table is saved on tape along with the program
itself. If the program is later loaded back into memory with the
CLOAD statement, the variable name table saved on tape will be
read into memory and will take the place of the existing variable
name table.
PEEK & POKE
The PEEK and POKE statements allow direct access to the Atari's
RAM. The Atari can include as many as 65,536 individual
addressable RAM memory locations. Each location is assigned a
number sequentially as its address, from to 65,536.
Every memory location can store a number in the range
through 255. As mentioned earlier, all data to be stored in
memory must be converted to a number in this range. The Atari
uses various coding strategies for converting BASIC keywords,
text data, numeric data, graphics displays, and machine language
into a form that can be stored in memory. The Atari knows how
to translate the contents in memory (numbers ranging from to
255) by the context in which that data is used.
The PEEK function allows the user toexaminethe valuestored in
the memory location named as its argument. For example, in the
following statement,
100 N = PEEK(1000)
the value stored at memory location 1000 will be assigned to the
variable N.
The POKE statement is used to place a value in a specified
memory location. POKE uses the following configuration,
84 User's Handbook to the Atari 400/800 Computers
POKE address, value
where the value specified is placed in the location given in
address, value and address can either be constants or variables.
For example, in the following statement,
100 POKE 2000, X
the value stored in variable X will be POKE'd into memory
location 2000.
The POKE statement cannot be used to change ROM. ROM is by
definition read-only memory, and cannot be altered with the
POKE statement.
Screen Output Prog r amming
The PRINT statement is used to display data on the screen. PRINT
statement output begins at the cursor's location. Therefore,
cursor positioning is the primary factor in sending output to the
screen.
As characters are output to the screen, the cursor position is
affected. Generally, the cursor moves one column to the right
after it has displayed a character. However, if a PRINT statement
ends with a carriage return, the cursor will move to the
beginning of the next display line. Also, escape sequences can
be used to move the cursor in a direction other than towards the
right hand side of the screen. Finally, the POSITION statement
can be used to move the cursor to any point on the screen. We
will cover each of these methods of cursor positioning as well as
other concepts of screen output programming in the next few
sections.
Using the Carriage Return in Cursor Positioning
The carriage return is generated by pressing the Atari's Return
key. The Return key generates the ASCII end-of-line (EOL)
character. This character causes the cursor to advance to the
beginning of the next display line. The EOL character can also be
generated by using the CHR$ function with 155 (the ASCII code
Advanced Atari BASIC 85
for EOL).
Tab Function
Tabbing on the Atari is very similar to tabbing on a normal
typewriter. Tabs are preset along the entire length of a logical
line. The first tab position is the left margin (column 2), followed
by columns 7, 15, 23, and every eighth column to the end of the
logical line.
Tabs work much like commas do when they are used as
formatting characters in PRINT statements. However, tabs and
commas function completely separately. The column positions
set up by commas have no effect on the tab positions, and vice
versa.
In the immediate mode, the tab key is used to move the cursor to
the next tab position. When the tab key is pressed, the cursor will
move to the next tab position without any of the characters it
passes over being erased. If the tab key is pressed with thecursor
at the last tab stop, the cursor will move to the start of the next
logical line.
In the program mode, the cursor is tabbed by using the ASCII
code for tab, 127. This can either be accomplished by using the
CHR$ function or by using ESC/TAB within a string.
In addition to the pre-defined tab stops already mentioned,
more tab stops can be set in any column desired. In the
immediate mode, a tab stop can be set by moving to the desired
column and pressing the SHIFT-TAB keys.
Tab stops can also be set with the PRINT statement. The PRINT
statement must display a string which causes the cursor to move
to the desired position. The tab set character, CHR$(159) or
ESC/SHIFT-TAB, must then occur in the string. For example, in
the following statement,
100 PRINT "JOHN"; CHR$(159)
a tab stop is set in the fourth column.
86 User's Handbook to the Atari 400/800 Computers
A tab stop can be cleared in the immediate mode by moving the
cursor to the position desired and then pressing CTRL-TAB. In
the program mode, a tab stop can be cleared by moving to the
desired column and displaying ASCII 158. This code can be be
displayed either with the CHR$ function or with ESC/CTRL-TAB.
One final point to keep in mind about tabstops is that whenever
a character is output in the space immediately preceding a tab
stop, that tab stop no longer has any effect.
Moving the Cursor with Escape Sequences
As mentioned earlier in this chapter, the cursor can be moved by
using the escape sequences for cursor control key sequence
within a PRINT statement string. For example, in the following
statement,
100 PRINT"— —JOHN JOHNSON"
the symbol — • represents pressing the following key sequence:
ESC/CTRL-*
This key sequence causes the cursor to move one position to the
left each time it is pressed.
Cursor control escape sequences can also be included in a
PRINT statement string by using the ASCII code for that
sequence with the ASC$ function. For example, in the following
statements,
100 DIM A$(10)
200 A$ = CHR$(29)
300 PRINT A$:PRINT A$:PRINT A$
the string variable A$ is set to the ASCII code for cursor down. In
line 300, the three PRINT statements cause the cursor to be
moved down 3 lines.
These cursor control sequences do not erase any of the
characters that they pass over.
Advanced Atari BASIC 87
Home Cursor
The home position can be defined as the upper left-hand corner
of the video display. The home cursor control sequence moves
the cursor to the position and erases all existing data on the
screen as well.
Home cursor is frequently used to position the cursor and erase
the screen in Atari BASIC. Home cursor can either be
accomplished by using the ASCII code for home cursor, 125,
with the CHR$ function, or by using either of the following
escape sequences:
ESC/CTRL- <
ESC/SHIFT-<
with the PRINT statements.
POSITION Statement
The POSITION statement can be used to place the cursor at any
location on thescreen. The POSITION statement is used with the
following configuration,
POSITION column, row
where column is the number of the column to be moved to, and
row is the number of the row to be moved to.
In actuality, the POSITION statement does not cause the cursor
to be moved. POSITION merely changes the values in the Atari's
memory where the cursor location is stored. When data is
subsequently displayed on thescreen, that data will be displayed
at these new display coordinates.
The display row number is stored in memory address 84, and the
column number is displayed in address 85. Thecontentsof these
locations can be examined with the PEEK function. For example,
the following statements,
PEEK (84)
PEEK (85)
88 User's Handbook to the Atari 400/800 Computers
will return the row and column numbers respectively.
When PRINT is used to output data to the screen, the previous
cursor position is stored in memory. Memory address 90
contains the last row number, and memory address 91 contains
the last column number. Again, the PEEK function can be used to
examine the contents of these memory addresses.
Remember, rows are numbered from to 23, and columns are
numbered from to 39.
Changing the Display Screen Margins
The standard left margin on the display screen is column 2. The
standard right margin is column 39. The Atari uses memory
address 82 to store the column number of the left margin, and
location 83 to store the column number of the right margin.
The POKE statement can be used to change either the left or
right margins. The following statements would reset the left
margin to column 5, and the right margin to column 30.
POKE 82, 5
POKE 83, 30
Screen Input Programming
Input programming is a vital part of BASIC programming. Nearly
every BASIC program requires some form of operator input. In
the following few sections, we will discuss programming
practices that are designed to make operator input efficient and
as error-free as possible.
Prompt Messages
One programming principle that should nearly always be
followed in input programming is to include a prompt message
with the INPUT statement. An example is given below.
100 PRINT "ENTER YOUR AGE";
200 INPUT AGE
Advanced Atari BASIC 89
In general, it is advisable to keep prompt messages as brief as
possible— as long as the message is clear to the user. Avoid
prompt messages which are overly wordy.
When long prompt messages are being used, it is a good practice
to place the prompt message on one line, and the input response
on the next line. For example, the following statement,
100 PRINT "ENTER OPERATION CODE (1 = ADD; 2 = DEL)"
200 INPUT X
would result in the following display:
Input Response Checks
A well-designed program should check the user's response to an
Input statement to be certain that no obvious input errors have
been made. If such an error was made, the program should
detect the error and force the user to re-enter the data.
Examples of input errors that can occur are numeric entries that
are outside of the allowed range, string entries that are longer
than allowed for by the Input statement's variable, and an input
90 User's Handbook to the Atari 400/800 Computers
response other than that prompted for.
The very nature of the Input statement prevents certain errors
from occurring as these are detected by the BASIC interpreter.
For example, if a numeric entry is made when a string variable is
specified with the Input statement, an error will occur. Likewise,
if a string entry is made when a numeric variable is specified with
the Input statement, an error will occur.
However, many Input entry errors will not be detected by the
BASIC interpreter. Serious errors can occur when the wrong
data is entered in response to an Input statement. It is a good
programming practice to check the operator's response to an
Input statement. This can either be accomplished with one or
more IF-THEN statements, or with ON-GOTO or ON-GOSUB
statements.
For example, in the following program, the operator's input is
checked with two IF-THEN statements. If the response is neither
of the following,
Y, N, y, n
the program will branch back to line 1200 for a new entry.
1000 DIM A$(20)
1100 PRINT
1200 PRINT "Enter Your Response (Y/N)"
1300 INPUT A$
1400 A$ = A$(1,1)
1500 IF A$ = "Y" OR A$ = "y" THEN 1800
1600 IF A$ = "N" OR A$ = "n" THEN 9999
1700 GOTO 1300
1800 REM Subroutine For 'Yes' Response
1900 PRINT "YES"
9999 END
CHAPTER 5.
ATARI BASIC REFERENCE GUIDE
This chapter provides descriptions and examples of the correct
syntax for Atari BASIC.
Each of the reserved words are listed in alphabetical order, along
with an appropriate abbreviation, if applicable.
The following notation will be used to describe the
configuration of each of the commands, statements, or
functions.
1. Capitalized words are keywords.
2. Items enclosed in brackets [ ] are optional.
3. Ellipsis (...) represents repetition.
4. Punctuation (except brackets) must be included as shown.
5. The following symbols will be used:
LN Line number
EX Algebraic or logical expression (i.e. X>5, 3 + X,
X = 7)
X, Y, Z Numeric variable name
X$, Y$, Z$ String variable name
a, b, c Any number or numeric expression
a$, b$, c$ String value
92 User's Handbook to the Atari 400/800 Computers
ABS
The ABS function returns the absolute value of its argument.
Configuration
X = ABS(a)
Example
PRINT ABS(-81)
81
ADR
The ADR function returns the memory address of the argument.
The argument must be a string variable or a string constant.
In BASIC, a machine language program can be put in a string
variable. However, the operating system moves variables around
to efficiently use memory. As a result, tocall a machine language
routine, the ADR function is used to locate the string.
Configuration
X = ADR(a$)
Example
X = ADR(B$)
AND
AND is used between two expressions, and returns the value 1 if
they are both true, and if either one is false.
CONFIGURATION
EX AND EX
Atari BASIC Reference Guide 93
The conditions of true and false are represented in the computer
by the logical values 1 and 0. As a result, the logical operators
(AND, OR, and NOT) generate only the values 1 and 0. The AND
operation can be explained by the following truth table.
EX1
EX2
RESULT
1
1
1
1
1
AND is generally used in an IF/THEN statement with relational
expressions. For example:
10 X = 10
20 Y = 30
30 IF X = 10 AND Y>100 THEN END
40 PRINT "CONDITIONS WERE NOT MET"
RUN
CONDITIONS WERE NOT MET
In this example, AND is used in an IF/THEN statement which
ends the program if both conditions are true. The first expression
of the AND statement is X =10. This is true because X is assigned
the value 10 in line 10. The second expression, Y>100, is false
because Y is assigned the value 30 in line 20. Asa result, EX1 is true
and EX2 is false. This corresponds to the truth table where EX1 =1
and EX2 = 0. The result from the table is (false), so the condition
of the IF/THEN statement is false, and the next line is executed.
The AND operator can also be used with algebraic expressions
like 5 * Y, 3 +X,X A 2, etc. However, these must also be converted
to logical or 1. The computer does this by assigning the logical
value to any expression that equals 0. Any expression thatdoes
not equal is assigned the logical value 1. For example, the
logical value of 5 * is 0. The logical values of 3 + 1, 2 A 2, 3 and
COS (45) are all 1.
94 User's Handbook to the Atari 400/800 Computers
Example
10 X =3
20 IF X A 2 AND 3 - X THEN END
30 PRINT "X IS EITHER 3 OR 0"
RUN
X IS EITHER 3 OR
This example uses AND in an IF/THEN statement that ends the
program if X squared and3-X both are not equal to zero. Since X
is assigned the value 3, the first part of the AND statement equals
3 squared. This is a logical 1 because 3 squared is non-zero.
However, the second expression, 3 - X, is equal to zero, which is
the logical 0. Since EX1 =1 and EX2 = 0, the AND statement is false,
and the next statement is executed (line 30).
ASC
The ASC function returns the ASCII code for the first character of
a string. The argument of ASC can be a string variable or
constant.
CONFIGURATION
X = ASC(a$)
EXAMPLE
10 DIM B$(10)
20 B$ = "ZEBRA"
30 PRINT ASC(B$)
RUN
90
ATN
The ATN function returns the arctangent of the argument. The
result will be in radians unless degrees are specified.
Atari BASIC Reference Guide 95
CONFIGURATION
X = ATN(a)
EXAMPLE
PRINT ATN(.576)
0.5225854816
BYE
BYE switches the system to the Memo Pad mode. The system has
no computing ability, and only the keyboard and display are
functional. The operator can experiment with the keyboard
without affecting the system. The system will return to BASIC
when the SYSTEM RESET key is pressed.
The operations of the computer and other devices (disk drive,
modem, etc.) are not at all affected by the Memo Pad. For
example, if a program is in memory, and a disk and modem are
being used, a BYE command will switch to Memo Pad. However,
SYSTEM RESET will restore the computer to BASIC, and all other
devices will still be ready to operate. The program in memory
will be unchanged.
CONFIGURATION
BYE
EXAMPLE
BYE
CLOAD (CLQA.)
The CLOAD command is used to load a previously recorded
program into the computer's memory. The program must have
been stored on a cassette with a CSAVE or SAVE command.
At the sound of the tone, press PLAY on the program recorder,
96 User's Handbook to the Atari 400/800 Computers
then press RETURN on the keyboard. The tape must be correctly
positioned before CLOAD is executed.
The CLOAD command clears the memory before the program is
loaded from the tape.
CONFIGURATION
CLOAD
EXAMPLE
CLOAD
CHR$
The CHR$ function returns the character with the ASCII code
specified by the argument. Although argument values can range
from to 65535, the ASCII code corresponds to the numbers
from to 255.
CONFIGURATION
X$= CHR$(a)
EXAMPLE
PRINT CHR$(65)
A
CLOG
The CLOG function returns the base 10 logarithm of the
argument.
CONFIGURATION
X =CLOG(a)
EXAMPLE
PRINT CLOG(4)
0.6020599914
Atari BASIC Reference Guide 97
CLOSE (CL.)
The CLOSE statement closes a channel that has been opened for
input, output, or both. However, closing a channel that has not
been opened will not cause an error.
The argument of a CLOSE statement must be the same as in the
corresponding OPEN statement. A channel that has been
opened for the use of a particular I/O device must be closed
before it is used for another device.
CONFIGURATION
CLOSE #a
EXAMPLE
CLOSE #3
CLR
The CLR command clears the values of the variables in the
memory. However, the variable name table remains unchanged.
As a result, the CLR command does not reduce the number of
variable names. After using CLR, all strings, arrays, and matrices
must be dimensioned again.
CONFIGURATION
CLR
EXAMPLE
CLR
98 User's Handbook to the Atari 400/800 Computers
COLOR (C.)
In graphics modes through 2, the COLOR statement is used to
choose the character that will be placed on the screen with a
PLOT statement.
CONFIGURATION
COLOR a
In all graphics modes, the argument of the COLOR statement
must be positive, and if it is not an integer, it will be rounded off.
In mode 0, the text is printed in the same color as the
background. Only the luminance of the color can be chosen. For
example, if the background is chosen to be green, the text must
be green, but it can be any brightness. The COLOR statement
indicates the character that is to be printed with the next PLOT
statement. In graphics mode 0, the COLOR statement has no
effect on the color of the character. Table 9-7 lists the characters
that correspond to the COLOR statement in graphics mode 0.
EXAMPLE
10 GRAPHICS
20 FOR I = 1 TO 5
30 READ X
40 COLOR X
50 PLOT 10 + I, 10
60 NEXT I
70 DATA 65, 84, 65, 82, 73
In the previous example, the word ATARI is printed at the center
of the display. Each data item is read individually at line 30, and
becomes the argument of the COLOR statement in line 40. The
loop is repeated 5 times, and each time the COLOR statement
has a different value as its argument. It can be seen from Table 9-
7 that in graphics mode 0, COLOR 65 indicates the character A.
After the COLOR 65 statement has been executed, any PLOT or
Atari BASIC Reference Guide 99
DRAWTO statement will be executed with the character A until
another COLOR statement has been executed.
EXAMPLE
10 GRAPHICS
20 COLOR 65
30 PLOT 0,0
40 DRAWTO 10,10
The preceding program would print the character A in the upper
left-hand corner of the screen because of the PLOT 0,0
statement. The DRAWTO 10,10 would cause a diagonal line
consisting of the character A to appear on the display. A
character would appear at the positions (0,0), (1,1), (2,2). ..(10,10).
The display looks like white characters on a blue background.
Actually, the "white" is very bright blue. The intensity of the
characters can be chosen with a SETCOLOR statement.
The COLOR statement has a different function in graphics
modes 1 and 2. Modes 1 and 2 have fewer characters available
than Mode 0, but each character can be printed in 4 colors.
The difference between modes 1 and 2 is the size of the
character. The characters in mode 2 are twice the height of mode
1, but are the same width.
Table 9-4 lists the values of the COLOR statement arguments for
each character in 4 colors. The columns of the table correspond
to the 4 color registers. The standard character set will be used
unless the alternate character set is specified with the statement
POKE 756, 226. To return to standard characters, POKE 756, 224.
100 User's Handbook to the Atari 400/800 Computers
EXAMPLE
10 GRAPHICS 1
20 FOR I = 1 TO 5
30 READ X
40 COLOR X
50 PLOT 6 + 1,0
60 NEXT I
70 DATA 65, 116, 193,114,73
The previous example displays the word ATARI at the top of the
display in three colors. The data is read at line 30 and becomes
the argument of the COLOR statement at line 40.
The COLOR statement chooses the character and the color
register to be used in the display. From Table 9-4, COLOR 65
indicates the character A in color register 0. COLOR 116
indicates the character T in color register 1.
The color registers are assigned specific information about the
color to be used. Color registers can be changed with a
SETCOLOR statement, but if no SETCOLOR statement is
executed, a standard set of default colors are used. The default
colors for graphics mode 1 and 2 are as follows:
COLOR REGISTER
DEFAULT COLOR
ORANGE
1
GREEN
2
BLUE
3
RED
A
BLACK
Color register 0-3 can be chosen for any character, but color
register 4 is used for the background and border.
In the previous example, the first character displayed was an A in
color register 0. Since no SETCOLOR was executed, the A will be
orange. The T will be green because COLOR 116 is in color
register 1.
Atari BASIC Reference Guide 101
If the same program was executed in the alternate character set,
by executing POKE 756, 226 after the GRAPHICS statement, the
word ATARI would appear in lower case letters. Also, in the
alternate character set, a "heart" character will appear in every
blank space. This occurs because the standard character set puts
a space (COLOR 32) in areas where no character has been
assigned. When the conversion to the alternate character set
occurs, COLOR 32 is interpreted as a "heart" in color register
(Table 9-4). As a result, an orange "heart" will appear in every
space except where the word ATARI appears.
In graphics modes 3 through 7, the COLOR statement is used to
choose the color register that will be used to plot points and
draw lines.
Graphics modes 3 through 7 are different from modes through
2 because modes 0, 1 and 2 are used to place characters on the
screen. Graphics modes 3 through 7 are used to place picture
elements (pixels) on the screen. A pixel is a rectangle that is
referred to by its coordinates (column and row) on the display. In
modes 3 through 7, the COLOR statement actually chooses a
color register, not a character.
EXAMPLE
10 GRAPHICS 3
20 FOR T= TO 3
30 COLOR T
40 PLOTT.O
50 NEXT T
The previous example displays the 4 colors of graphics mode 3.
Line 40 plots a pixel at column T, row 0. The color of the pixel is
determined by the last COLOR statement. The first time through
the program, T is set equal to at line 20. Line 30 indicates that
color T is used. Since no SETCO LOR statement was executed, the
default colors are used.
102 User's Handbook to the Atari 400/800 Computers
GRAPHICS MODES 3, 5, and 7
COLOR NUMBER DEFAULT COLOR
ORANGE
1
GREEN
2
BLUE
3
BLACK
Asa result, when T = 0, the color is orange. The PLOT statement at
line 50 colors the pixel at col umnO, row orange. The next pixel,
at column 1, row is colored green. The pixel at column 2, rowO
is blue and the next one is black.
In graphics modes 4 and 6, the COLOR statement is used in the
same fashion as in graphics modes 3, 5, and 7. However, modes4
and 6 have only two colors, and the default colors are as follows.
GRAPHICS MODES 4 and 6
COLOR NUMBER DEFAULT COLOR
BLACK
1 ORANGE
Graphics mode 8 has only one color, with two brightness levels.
As a result, the COLOR statement is used to select the brightness
of a pixel. In other words, COLOR 1 causes the next plotted pixel
to be visible. COLOR causes the next plotted pixel to be the
same as the background.
In graphics mode 8, the pixels are very small, and the graphics are
slow. It sometimes is useful to draw an entire area, then "erase"
what is not wanted. This is often faster than drawing only what is
wanted. This can be done by drawing an area using COLOR 1,
then "erasing" by using COLOR 0.
COM
COM is used interchangeably with DIM in dimensioning strings,
arrays, and matrices.
Atari BASIC Reference Guide 103
CONFIGURATION
COM X i a[b])
^ X$(a)
Y(c[d,
Y(c)
EXAMPLE
COM B$(50), A(10,10)
CONT (CON.)
The CONT command causes a program which had been stopped
to continue execution at the next numbered line. A program will
be stopped because of an error, SYSTEM RESET, BREAK, END, or
STOP.
In any situation, the use of CONT will cause the rest of the
current line of code to be ignored. As a result, executing BREAK
and CONT during a program may cause serious problems. When
a program is stopped using BREAK, there is no way to be sure the
program will resume where it was stopped. Important steps may
be interrupted or skipped, and loops may be improperly exited.
A program can be continued after an error, but the entire line of
the error will be skipped.
A program can be continued after a SYSTEM RESET, but this will
generally have negative results. All I/O channels will be closed,
the computer will return to the immediate mode, the screen will
be cleared, graphics mode will resume, etc.
CONFIGURATION
CONT
EXAMPLE
CONT
104 User's Handbook to the Atari 400/800 Computers
COS
The COS function returns the cosine of its argument. The
argument will be assumed in radians unless a DEG statement
precedes the COS statement.
CONFIGURATION
X = COS(a)
EXAMPLE
10 DEG
20 X = COS(180)
30 PRINT X
RUN
-1
CSAVE (CS.)
The CSAVE command is used to copy the program in the
computer's memory on cassette tape. Only CLOAD can be used
to read a program that was stored using CSAVE.
When the tape is properly positioned, enter CSAVE. The tone
will sound twice as a signal to press the cassette recorder's PLAY
and RECORD keys, followed by pressing RETURN on the Atari
keyboard.
If channel 7 is open for another device, an error will occur, but
the channel will be closed. A repeat of CSAVE will then be
successful.
CONFIGURATION
CSAVE
EXAMPLE
CSAVE
Atari BASIC Reference Guide 105
DATA (D.)
The DATA statement supplies a list of information that is used in
a program through READ statements. A DATA statement can
include numeric values, string values, or both. String variables
must have been dimensioned before being read.
Data items are separated by commas. Therefore, string values
that contain commas will be read as separate data items. For
example, DATA DOE, JOHN is a DATA statement with two data
items. However, DATA DOE. JOHN has only one item.
CONFIGURATION
DATA a$
,b
,b$
Data must be read into the correct type of variable. A string
variable can accept data in any form.
EXAMPLE
10 DIM A$(20)
20 FOR 1 = 1 TO 5
30 READ A$:? A$
40 NEXT I
50 DATA TOM C, 25„3 + 4 *
%,247
RUN
TOM C.
25
3 + 4 * %
247
The preceding example shows correct data for a string variable.
Notice the blank line in the output that corresponds to the two
commas in a row. This is read as a string value with nocharacters
and length equal to zero.
If only 4 data items had been supplied with this program, the
message: ERROR-6 AT LINE 30 would have been displayed to
106 User's Handbook to the Atari 400/800 Computers
notify the user that not enough data was supplied.
Numeric variables can only accept numbers as input. Standard
notation and scientific notation are both acceptable. For
example, 3.14159266, 2.85E-10, .0001, 35 and -45 are all
acceptable data items. Expressions will not be evaluated. They
will cause an Input Statement Error (#8). Numeric data must not
include commas.
EXAMPLE
10 DIM A$(10)
20 FOR I = TO 4
30 READ A$, A
40 PRINT A$, A
50 NEXT I
60 DATA PENCILS, 20,PENS,25,RULERS,40,ERASERS,50,
PAPER,200,GLUE,5
The preceding example shows a correct sequence for reading
string and numeric data into correct variables. However, the
READ statement is only called 5 times, and there are 6 sets of
data. This will not cause an error, but the last set of data (GLUE,5)
will never be read.
DATA statements can appear anywhere in a program, even after
an END statement, However, any statement that follows a DATA
statement on the same line will not be executed.
Data can only be read once unless a RESTORE statement is
executed. The correct use of RESTORE is also explained in this
chapter.
PEG (PE.)
The DEG statement causes the trigonometric functions to be
performed in degrees instead of radians. The functions will be
performed in radians until degrees are specified. Also, radians
will be used after a SYSTEM RESET, NEW, or RUN command.
Atari BASIC Reference Guide 107
CONFIGURATION
DEG
EXAMPLE
10 DEG
20 PRINT SIN(90)
RUN
1
The example shows that the sine of 90° is 1. If the DEG statement
was not present, the result would be 0.8939970243.
DIM (PI.)
The DIM statement is used to set aside memory space for strings
and 1 or 2 dimensional arrays. Two dimensional arrays, or
matrices, can be used to make tables of values.
CONFIGURATION
DIM
X(a[,b])
X$(a)
,Y(c[,d])
,Y$(c)
A DIM statement can include any combination of numeric and
string variable dimension statements. For example, DIM
A(10,10), B(9), A$(90), B$(90) dimensions all four variables in one
statement.
A string variable can contain only one string. The dimension of a
string variable indicates the maximum number of characters that
the string variable can contain.
108 User's Handbook to the Atari 400/800 Computers
EXAMPLE
10 DIM A$(10)
20 READ A$
30 PRINT A$
40 DATA INDEPENDENCE DAY
RUN
INDEPENDEN
The preceding example shows that the string variable A$ is
dimensioned to 10 characters at line 10. However, during the
program, A$ is assigned a 16 character string with the READ
statement at line 20. Since room for only 10 characters was set
aside in memory, only the first 10 characters of the DATA item
are assigned to A$. The PRINT statement in line 30 displays the
contents of A$. It can be seen from the output that A$ only has 10
characters.
The DIM statement must be executed before an INPUTor READ
occurs. If the DIM statement of the previous example was
deleted, the following message would occur.
ERROR-9 AT LINE 20
If a variable is dimensioned twice in the same program (without
CLR), ERROR-9 occurs.
The maximum size of string variables depends on the amount of
available memory at the time of the DIM statement.
Dimensioning numeric variables determines the number of
elements that the variable can contain, not the length. A
subscript is the number that follows a variable name (in
parentheses) and indicates which element of that variable is
considered. The following example shows howtoassign4values
to a subscripted variable.
Atari BASIC Reference Guide 109
EXAMPLE
10 DIM X(3)
20 FOR I = TO 3
30 READ X:X(I) =X
40 PRINT X(l),
50 NEXT I
60 DATA 12, 14, 13, 15
RUN
12 14 13 15
Notice that 4 values can be assigned to a variable that has a
dimension of 3. This is possible because each array's initial
element has a subscript of 0. The array can be represented as a
table of values as shown in the following illustration.
12
14
13 | 15
The number in the DIM statement indicates the largest subscript
that can be used.
It should be noted from the example (line 30) that subscripted
variables cannot be used in a READ statement. As a result, a
separate statement is needed to assign the subscripted variable.
The assignment statement can be on the same line (as shown
here) or on a separate line.
Numeric variables can also be used with two subscripts. This
results in a two dimensional array, or matrix. For example, if X is
dimensioned in the statement DIM X(3,2) the following table
would result.
1
2
110 User's Handbook to the Atari 400/800 Computers
DOS (DO.)
CONFIGURATION
DOS
EXAMPLE
DOS
The DOS command is used to display the DOS utilities Menu.
DOS must be present if the DOS command is to be used. If DOS
is not present, the system will be put into the Memo Pad mode.
To return to BASIC from Memo Pad, press SYSTEM RESET.
When the DOS command is executed, all I/O channels will be
closed except channel 0. The display is cleared and the sound
voices are shut off. Also, the color registers resume their default
values.
The Disk Operating System Menu is a list of 15 disk functions.
There are two versions of the Disk Operating System, version 1.0
and version 2. OS. The DOS command has a different effect in
each of the two versions.
In version 1.0, the DOS Menu appears on the display as soon as
DOS is executed.
DISK OPERATING SYSTEM 9/24/79
COPYRIGHT 1979 ATARI
A. DISK DIRECTORY I. FORMAT DISK
B. RUN CARTRIDGE J. DUPLICATE DISK
C.
COPY FILE
K.
BINARY SAVE
D.
DELETE FILE(S)
L.
BINARY LOAD
E.
RENAME FILE
M
RUN AT ADDRESS
F.
LOCK FILE
N.
DEFINE DEVICE
G.
UNLOCK FILE
O.
DUPLICATE FILE
H.
WRITE DOS FILE
Atari BASIC Reference Guide 111
A program that is in memory will not be affected by a DOS
statement in version 1.0. However, disk operations J or O will
erase the contents of the memory. For example, if a program is in
memory, and a DOS command is executed, followed by
DUPLICATE DISK or DUPLICATE FILE, the program will be gone
when the system returns to BASIC.
DISK OPERATING SYSTEM II
COPYRIGHT 1980 ATARI
VERSION 2.0S
A. DISK DIRECTORY
B. RUN CARTRIDGE
C. COPY FILE
D. DELETE FILE(S)
E. RENAME FILE
F. LOCK FILE
G. UNLOCK FILE
H. WRITE DOS FILES
I. FORMAT DISK
J. DUPLICATE DISK
K. BINARY SAVE
L. BINARY LOAD
M. RUN AT ADDRESS
N. CREATE MEM.SAV
O. DUPLICATE FILE
In DOS 2.0, DOS consists of 2 files, DOS.SYS and DUP.SYS.
DUP.SYS must be present on the diskette in drive 1 or the Atari
will return to BASIC. DUP.SYS was a portion of memory where
BASIC programs normally reside. In order to save any BASIC
program residing in this area of memory, the Atari will save that
program onto the MEM.SAV file on drive 1— if that file exists.
Once these operations have been completed, the DOS utilities
menu will appear. You can return to BASIC by choosing menu
item B or by pressing the System Reset key.
112 User's Handbook to the Atari 400/800 Computers
PRAWTO (DR.)
The DRAWTO statement is used in the graphics modes to drawa
line. The arguments of the DRAWTO statement indicate the
column and row where that line ends.
CONFIGURATION
DRAWTO a,b
Both arguments of a DRAWTO statement must be positive, and if
they are not integers, they will be rounded off. The arguments
must also lie within the range of the display. For example,
GRAPHICS 3 has 40 columns and 20 rows. DRAWTO 40,20 would
result in ERROR-141. Since the columns are numbered to 39
and the rows are numbered to 19, DRAWTO 40, 20 contains
arguments which lie outside the range of display.
A DRAWTO statement must occur after a PLOTstatement. PLOT
determines the starting point of the line, and DRAWTO
determines the end point. A DRAWTO statement can follow
another DRAWTO statement, if the first DRAWTO is preceded
by a PLOT statement.
EXAMPLE
10 GRAPHICS 3
20 COLOR 1
30 PLOT 5,5
40 DRAWTO 10,5
50 DRAWTO 10,10
60 DRAWTO 5,10
70 DRAWTO 5,5
A DRAWTO statement that follows another DRAWTO statement
will use the end of the last line to start the new line. The previous
example began by plotting a point at line 30, then proceeded to
Atari BASIC Reference Guide 113
draw the 4 sides of a square in Lines 40, 50, 60, and 70.
The DRAWTO statement can also be used in graphics modes0,1,
and 2. However, the PLOT statement in the text modes (0, 1 and
2) places a character on the display. The COLOR statement
determines the character that is printed (Tables 9-7 and 9-4). Asa
result, the DRAWTO statement in the text mode creates a line of
characters.
EXAMPLE
10 GRAPHICS 2
20 COLOR 65
30 PLOT 0,0
40 DRAWTO 9,9
The previous example specifies graphics mode 2 in line 10. Line
20 indicates the character that appears on the display (Table 9-4).
The PLOT statement in line 30 places an orange, uppercase A at
column 0, row 0. The DRAWTO statement makes a diagonal
line, consisting of the character A. The characters appear at the
positions (0,0), (1,1),(2,2),...(9,9).
The line drawn with a DRAWTO statement iseither composed of
picture elements or characters. When a diagonal line is drawn
using PLOT and DRAWTO, the line appears in steps. This occurs
because the line is drawn with characters or picture elements
that are relatively large.
A "line" drawn with PLOT and DRAWTO.
114 User's Handbook to the Atari 400/800 Computers
END
An END statement ends the execution of the program. An END is
not necessary at the end of a program because execution stops
automatically after the last line of code. However, it is good
programming technique to end BASIC programs with an END
statement.
CONFIGURATION
END
When an END statement is executed, all I/O channels will be
closed except 0, the display will be set to graphics mode 0, and all
sound will be turned off.
EXAMPLE
10 INPUT X
20 IF X<=10THEN END
30 PRINT "X IS LARGER THAN 10"
40 GOTO 10
The previous example will end only if a value of X is entered
which is less than or equal to 10.
ENTER
ENTER is used to recover programs that have been saved on a
cassette or disk. ENTER can only be used to load programs that
were saved with the LIST statement.
CONFIGURATION
ENTER device[:filespec]
When an ENTER statement is executed, the computer's memory
is not erased. As a result, the new program being loaded will be
put into memory together with any existing program lines. For
Atari BASIC Reference Guide 115
example, if the program in memory contained line numbers 10,
20, 30..., and the program being loaded (using ENTER) contained
line numbers 5, 15, 25, 35,..., the resulting program in RAM
would include the line numbers from each of the two programs.
ENTER does not alter the program in memory unless the
program being entered has the same line numbers as the
program being loaded. For example, if the program in memory
contains line numbers 10, 20, 30, 40, 50, and 60 and the program
being entered contains 10, 20, 30, 45, 55, 70, 80, and 100, the new
program in memory will contain all of the newly entered
program, but only lines 40, 50, and 60 of the original program.
The original lines 10, 20, and 30 in RAM will be replaced with
lines 10, 20, and 30 being loaded from cassette or disk. Lines 40,
50, and 60 of the original program remain unchanged.
ENTER is the only Atari BASIC statement that can recover a
program without clearing the memory first.
When ENTER is used with the program recorder, the tape must
be in the correct position prior to execution. When the ENTER
statement is executed, the tone will sound once to remind the
operator to press PLAY on the recorder. The recorder will be
activated after the RETURN key on the keyboard has been
pressed.
When ENTER is used with a disk, the DOS must have been
booted first. If more than one disk is being used, the number of
the disk must be specified.
EXAMPLES
ENTER "C"
ENTER "D2:JONES"
EXP
The EXP function returns the exponential of the argument. The
exponential is the value of e(2.71828179...) raised to the powerof
the argument.
116 User's Handbook to the Atari 400/800 Computers
CONFIGURATION
X = EXP(a)
EXAMPLE
PRINT EXP(5)
148.413155
FOR (F.)
A FOR statement is used with a NEXT statement to form a
repetitive loop within a program.
CONFIGURATION
FOR A = a TO b [STEP c]
Every FOR statement must have a corresponding NEXT
statement.
EXAMPLE
10 FOR I =1 TO 5
20 PRINT I;
30 NEXT I
RUN
12345
In the previous example, the FOR/NEXT loop is repeated five
times. Line 20 is the only statement inside the loop, however, any
number of program lines can be placed within a loop.
In line 10, I is assigned the value 1. I is referred to as a counter.
The value of I is incremented where a NEXT I statement is
executed. Here, the program returns to the FOR statement,
where I is incremented by one. This loop is repeated until I isset
equal to 5. When the counter (I) has been set equal to the value
(5), the loop has been executed, the program will proceed with
the statement following NEXT I.
Atari BASIC Reference Guide 117
A FOR/NEXT loop can use a STEP statement to increment the
counter by a value other than 1.
EXAMPLE
10 FOR J =1 TO 2 STEP .5
20 PRINT J,
30 NEXT J
RUN
1 1.5 2
The preceding example contains a FOR/NEXT loop which
increments the value of J by .5 each time the loop is executed.
A FOR/NEXT loop can also be used to decrease the value of the
counter. This can be accomplished by using the optional STEP
statement within the FOR statement. If the STEP statement has a
negative argument, the counter is decreased each time the loop
is executed. The following example illustrates a FOR/NEXT loop
where the counter is decremented rather than incremented.
EXAMPLE
10 FOR K =10 TO 5 STEP -2
20 PRINT K,
30 NEXT K
RUN
10 8 6
This loop begins at line 10 by assigning the counter (K) the value
10. At line 20 the value of K is printed. When line 30 is
encountered, execution continues at line 10, because the NEXT
statement returns the program to the preceding FOR statement.
The value of the counter is changed by the argument of STEP.
Since the STEP value is -2, the counter is decreased by 2. The
value of the counter is changed to 8. At line 20, the new value of
K is printed. Line 30 is executed again, so the program returns to
the FOR statement at line 10. The counter is again decremented
by 2. The new value of K is 6. At line 20, this K value is printed.
When line 30 is executed again, the program does not return to
118 User's Handbook to the Atari 400/800 Computers
line 10. The current value of the counter is 6, and if the counter
was to be decremented again,the counter would be4. However,
4 is less than the final value which is specified in the FOR
statement (the argument of TO). As a result, the loop does not
continue after K =6 because another decrement would make the
counter less than the final value (5).
If the counter of a loop is being incremented, the loop will be
executed until the counter would exceed the final value if it
were incremented again. For example: FOR J = 1 TO 4 STEP 2
would be executed with J equal to 1 and 3. The counter (J) would
exceed the final value (4) if it were incremented again.
A FOR/NEXT loop should be executed as if it were a single
statement. An attempt to branch into a FOR/NEXT loop will
cause an error.
EXAMPLE
10 GOTO 30
20 FOR I =1 TO 10
30 PRINT I
40 NEXT I
RUN
ERROR- 13 AT LINE 40
In general, branching out of a FOR/NEXT loop will not cause an
error. However, exiting a loop before it has completed should be
avoided.
FRE
The FRE function returns the number of bytes of memory
available. The FRE function requires an argument, but that
argument has no effect on the value returned.
CONFIGURATION
X = FRE (a)
EXAMPLE
PRINT FRE(0)
Atari BASIC Reference Guide 119
GET (CE.)
The GET function reads 1 byte from a channel that has been
opened for input. GET is used with the keyboard, display,
Program Recorder, or disk.
CONFIGURATION
GET #a, X
The first argument of a GET statement indicates the I/O channel
that will be used. If the first argument is not an integer, it is
rounded off. The second argument names the variable that will
be assigned the value read from the channel. This value will be
an integer between and 255.
For example, if data is being accepted from the Program
Recorder, the GET statement must be preceded by an OPEN
statement. The OPEN statement must include the number of the
I/O channel, the device name, and an input operation code.
Numbers that are not integers are rounded off.
EXAMPLE
10 OPEN #3,4, 0, "C"
20 FOR J = 1 TO 100
30 GET #3, X
40 PRINT CHR$(X)
50 NEXT J
60 CLOSE #3
The previous example shows the correct format for using a GET
statement. Line 10 opens the I/O channel and specifies channel
#3 for input with the Program Recorder. The channel number
can be any number from 1 through 7, but the channel must not
be open for another device. The second argument of the OPEN
statement (4) indicates that the device will be used for input.
Line 20 is the first line of a FOR/NEXT loop. The loop ends with
the NEXT statement at line 50. The initial value of the counter (J)
120 User's Handbook to the Atari 400/800 Computers
is 1, and the final value is 100. The counter is incremented by 1
each time the loop is executed, so the loop will be executed 100
times. Lines 30 and 40 both appear inside the loop (between FOR
and NEXT). As a result, lines 30 and 40 are repeated 100 times.
Each time line 30 is executed, an integer between and 255 is
assigned to the variable X. Line 40 prints the character that has
the ASCII code specified by X. Line 60 closes the I/O channel.
GET is used with the disk in the same fashion as it is used with the
Program Recorder. However the OPEN statement must include a
file specification. The first argument of the OPEN statement is a
channel number. Any channel from 1 to 7 can be used if it is not
already open. The second argument is the operation being
performed. GET can be used with the disk if the OPEN statement
has a second argument of 4 (input) or 12 (input and output). For
example, OPEN #2, 12, 0,"D:BUDGET" is a correct OPEN
statement for using GET with a disk. GET assigns the next byte
read from the disk to the variable specified in the GET statement.
The GET statement can also be used with the keyboard. An OPEN
statement must be executed before the GET statement is
encountered. The first argument of the OPEN statement is the
number of a channel that is not already OPEN. The channel
number must be a number from 1 to 7. The second argument of
the OPEN statement must be 4 (input). The third argument is
generally 0. The device code "K" is the fourth argument.
With the keyboard, a GET statement causes the program to wait
for one keystroke. When a key (or combination of keys) is
pressed, the ASCII code of the character is assigned to the
variable in the GET statement.
EXAMPLE
10 OPEN #2, 4, 0, "K"
20 GET #2, X
30 PRINT X
40 CLOSE #2
RUN
(PRESS "S")
83
Atari BASIC Reference Guide 121
The previous example consists of a program that uses the GET
statement with the keyboard. Line 10 opens channel #2 for the
keyboard input. In line 20, the GET statement assigns the ASCII
code of a character to the variable X. Line 30 displays the ASCII
code on the screen. When the program is executed, line 10
opens the I/O channel, but the program waits at line 20. When
the next keystroke occurs, the program continues. In this
example, the keystroke is the S key. The ASCI I code of S is 83, so X
is assigned the value 83. Line 30 causes 83 to be printed on the
display, and line 40 closes the I/O channel.
The GET statement can also be used with the display. An OPEN
statement must precede the GET statement. The OPEN
statement specifies an I/O channel that is not currently open.
The channel number must be from 1 to 7. The second argument
must be 4 (input) or 12 (input and output), and thedevice must
be "S". With the display, the position of the cursor determines
the character or picture element to which the GET statement
applies. The GET statement retrieves the COLOR information at
that point.
In graphics modes 0, 1, and 2, the COLOR information indicates
a character (and color register). Tables 9-4 and 9-7 list the
COLOR values for graphics modes 0, 1, and 2. In graphics modes
3 through 8, the GET statement indicates the color of the picture
element where the cursor is located. The value that a GET
statement retrieves is assigned to the variable in the GET
statement. The cursor advances to the next position after a GET
statement has been executed. An attempt to execute a GET
statement when the cursor is at the last column of the last row
results in an error.
EXAMPLE
10 OPEN #3, 4, 0, "S"
20 GRAPHICS 2
30 COLOR 65
40 PLOT 0,0
50 POSITION 0,0
60 GET #3, X
70 PRINT X
80 CLOSE #3
122 User's Handbook to the Atari 400/800 Computers
The previous example consists of a program that uses GET with
the display. Line 10 opens I/O channel #3 for input from the
display (device "S"). Line 20 specifies graphics mode 2. Line 30
indicates the character and color that is displayed. Table 9-4 lists
the COLOR codes for graphics mode 2. COLOR 65 indicates an
upper case A in color register 0. Since SETCOLOR is not used in
this program, the character is orange, the default color. The
PLOT statement at line 40 places the character at the upper left
corner of the display. Line 50 moves the cursor to the same
position as the character (0,0). The GET statement at line 60
assigns the COLOR information to the variable X. The channel
number in the GET statement must be the same as the channel
number in the OPEN statement. Line 70 displays the COLOR
information (65) on the display, and line 80 closes the I/O
channel.
GET can also be used with the screen editor (device "E"). The
OPEN statement must include an unused I/O channel number.
Also, the OPEN statement must have operation code4 (input) or
12 (input and output). Since the screen editor uses the keyboard
for input, the GET statement has nearly the same function with
devices "K" and "E". The GET statement assigns the ASCII codeof
a keystroke to the variable specified in the statement. The
program waits for input from the keyboard before it continues.
However, when a GET statement is executed, the character from
the keyboard must be followed by RETURN.
EXAMPLE
10 OPEN #3, 4, 0, "E"
20 GET #3, X
30 PRINT X
40 CLOSE #3
RUN
(Press "S" followed by RETURN)
83
In the previous example, line 10 opens channel #3 for in put from
the screen editor. When the screen editor is accessed, the screen
is cleared. The program will wait at line 20 for input from the
keyboard. If more than one character is entered, an error results.
Atari BASIC Reference Guide 123
The GET statement only accepts one character, followed by
RETURN. If only one character is entered, the GET statement
assigns the ASCII code of that character to the variable X. Line 30
displays the value of X which is 83, since the ASCII code of Sis 83.
Line 40 closes the I/O channel.
GOSUB (COS.)
GOSUB branches program control to the subroutine beginning
at the line number specified by its argument.
CONFIGURATION
GOSUB LN
Subroutines can be called from any part of a program. A RETURN
statement, at the end of a subroutine, causes the program to
resume execution with the statement directly after the GOSUB
statement.
Subroutines are convenient to use when the same set of
operations need to be repeated at different parts of a program.
EXAMPLE
10 FOR J =0TO 2
20 GOSUB 100
30 NEXT J
40 J =5
50 GOSUB 100
60 END
100 PRINT J;
110 RETURN
RUN
0125
The previous example illustrates a subroutine that is called 4
times, from 2 different parts of the program. In this example,
only one statement is included in the subroutine. However,
many statements can be included in a subroutine.
124 User's Handbook to the Atari 400/800 Computers
Line 10 begins a FOR/NEXT loop. The counter (J) is set equal to
the first time through the loop. Line 20 calls the subroutine at line
100. As a result, line 100 is executed next. The subroutine prints
the value of J and proceeds to line 110. At line 110, the program is
returned to the point where the subroutine was called (line 20).
The statement at line 30 is then executed. The NEXT statement
causes the loop to be incremented and repeated. The counter (J)
is set equal to 1, and the subroutine is called again from line 20.
At line 100, the value of J is printed. Line 110 returns the program
to line 20.
These steps are also repeated for J = 2. When the loop has been
executed 3 times, the program will proceed to line 40. J is
assigned the value 5, and the subroutine is called again at line 50.
The subroutine prints the value of J. The program then returns to
line 60 where it ends.
GOSUB can also be used with ON to branch a program to one of
several subroutines.
CONFIGURATION
ON EX GOSUB LN [,LN] [,LN]...
The expression after the ON statement indicates which line
number the program proceeds to. This is called the control
expression. The control is evaluated and rounded off. If the
value is negative or greater than 255, an error occurs. If the value
of the control is 1, the program continues at the first line number
after GOSUB. If the control is equal to 2, the program continues
at the second line number after GOSUB, etc.
If the value of the control is or greater than the number of line
numbers, the line after the ON/GOSUB statement is executed.
EXAMPLE
ON X GOSUB 100, 200, 300, 400
This statement executes the subroutine at line 100 if X = 1. If X=2,
Atari BASIC Reference Guide 125
the subroutine at line 200 is executed. If X =3, the subroutine at
line 300 is executed. If X = 4, the subroutine at line 400 is
executed. If X = or X is greater than 4, the next line is executed.
GOTO
The GOTO statement causes the program to proceed at the
indicated line number.
CONFIGURATION
GOTO LN
EXAMPLE
10 X =X + 1
20 IF X A 2=>50THEN END
30 PRINT X;
40 GOTO 10
RUN
1234567
The previous example demonstrates the use of GOTO. Line 10
increases the value of X by 1. Line 20 ends the program when X
squared is greater than 50. When line 40 is executed, the
program returns to line 10. This program repeats lines 10 through
40 until the program is ended or branched out of the loop. The
program ends when X = 8 because 8 squared is greater than 50.
GOTO is also used with an ON statement to branch a program to
one of several lines.
CONFIGURATION
ON EX GOTO LN [,LN] [,LN]...
The expression after the ON statement indicates which line
number the program proceeds to. This is called the control
expression. The control is evaluated and rounded off. If the
value is negative or greater than 255, an error occurs. If the value
of the control is 1, the program continues at the first line number
126 User's Handbook to the Atari 400/800 Computers
after GOTO. If the value is 2, the program continues at the
second line number after GOTO, etc.
EXAMPLE
10
FOR I =
1 TO 3
20
ON I GOTO 40, 50, 60
40
PRINT"
I =1":GOTO70
50
PRINT"
I =2":GOTO70
60
PRINT"
I = 3"
70
NEXT I
GRAPHICS
GRAPHICS sets one of the graphics modes.
CONFIGURATION
GRAPHIC a
The GRAPHICS statement generally clears the screen display
upon execution. By adding 32 to the GRAPHICS statement
argument, this feature is suppressed.
In graphics modes 1 through 8, a four line text window appears in
the bottom of the display. By adding 16 to the GRAPHICS
statement argument, the text window will be suppressed.
EXAMPLE
GRAPHICS 49
The preceding GRAPHICS statement sets graphics mode 1 with
the screen clearing and text window features suppressed.
]F
The IF statement is used with a THEN statement to branch a
program if a particular condition is true.
CONFIGURATION
._ rv -r,. rK . statement . . .
IF EX THEN ... ^statement ...
LN L J
Atari BASIC Reference Guide 127
The expression (EX) that follows IF can be logical or algebraic.
Any algebraic expression that does not equal zero is considered
true. The logical operators (AND, NOT and OR) can be used in
the IF expression.
EXAMPLE
10 X = 15
20 Y = 30
30 IF X>10 AND Y>20 THEN 50
40 PRINT "CONDITIONS NOT MET":END
50 PRINT "CONDITIONS HAVE BEEN MET"
RUN
CONDITIONS HAVE BEEN MET
The previous example shows two logical expressions and a
logical operator in the IF/THEN statement (line 30). The AND will
only be true when both conditions have been met. Since X = 15
(line 10) and Y =30 (line 20), both of the conditions of line 30 are
true. As a result, the program branches to line 50. At line 50, the
message CONDITIONS HAVE BEEN MET is printed.
An END statement is used in line 40 to prevent both messages
from being printed when the IF statement is false.
An IF/THEN statement can also be followed by statements
instead of a line number.
EXAMPLE
10 Y =5
20 X =10
30 IF X<100 THEN PRINT X:PRINT Y
RUN
10
5
The previous example shows that statements can follow a THEN
statement, separated by colons. If the condition is true, the
statements are executed. If the condition is false, the program
will continue at the next line, and the statements after the THEN
statement are ignored. Since X =10 (line 20), the condition at line
128 User's Handbook to the Atari 400/800 Computers
30 (X<100) is true. As a result, the statements after THEN are
executed, and the values of X and Y are printed.
The following example illustrates the use of algebraic
expressions. An algebraic expression is true when it does not
equal zero.
EXAMPLE
10 FOR I =-2 TO 2
20 IF NOT I THEN END
30 PRINT I
40 NEXT I
RUN
-2
-1
The previous example contains a program that ends when a
condition is true. The condition is NOT I. NOT I is true when I is
false, and I is false when I is set equal to zero. When I has any
value other than zero, it is true.
Line 10 begins a FOR/NEXT loop. The first time the loop is
executed, I is set equal to -2. Line 20 is an IF/THEN statement
with the condition NOT I. When I is set equal to -2, it is
considered true because it is not equal to zero. Since I is true,
NOT I is false.
The condition at line 20 is false, so the program does not end.
Line 30 is executed next, so the value of I is printed. Line 40
returns the program to line 10, where the counter (I) is
incremented by 1. I is set equal to -1, so I is still true. Since I is
true, NOT I is false. The condition of line 20 fails, so the value of I
is printed.
When the loop is executed the third time, I is set equal to zero. I
is false, so NOT I is true. Since NOT I is true, the program is ended
at line 20.
Atari BASIC Reference Guide 129
INPUT (I.)
The INPUT statement causes data to be assigned to variables.
CONFIGURATION
INPUT [#aj x *
,Y
,Y$
The INPUT statement is generally used with the keyboard,
editor, disk, or Program Recorder. The INPUT statement
requires an I/O channel number as well as a previous OPEN
statement if any device other than the editor is used.
The correct format for numeric data is standard notation or
scientific notation. Spaces can appear before or after a numeric
value, but spaces within a numeric value cause an error. Numeric
data can be entered on the same line, separated by commas.
EXAMPLES
54, 4E5, -10
-3.45E-10
0,1,1,5,3,10
Expressions cannot be used as numeric data with INPUT. Any
format other than standard floating point decimal or scientific
notation causes an error.
Each line of numeric data must be followed by an end-of-line
character (RETURN).
String data must also be followed by an end-of-line character.
Only one string data item can occur on a line. Also, a string data
can be read only into dimensioned string variables. If the length
of a data item is more than the dimensioned length of the
variable, the excess characters are eliminated, but no error
occurs. Any character can be a part of a string data item for
INPUT (including commas and special graphics characters).
130 User's Handbook to the Atari 400/800 Computers
When INPUT is used with the screen editor, no OPEN statement
is necessary. The program waits for input from the keyboard
when an INPUT statement is executed. A question mark (?)
appears on the screen to remind the operator to enter data.
EXAMPLE
10 DIM X$(10)
20 INPUT X, X$
30 PRINT X$, X
RUN
? 45, JONES, BILL
JONES, BILL 45
In the previous example, line 10 dimensions the string variable
for 10 characters. Line 20 is an INPUT statement that requests a
numeric value to assign to X, and a string value to assign to X$.
When the program is executed, the INPUT statement causes the
program to wait at line 20 for input.
Since no I/O channel is specified, the input isaccepted from the
keyboard, and the prompt (?) is displayed. The user responds
with two data items. The value 45 is entered for a value of X. The
string value JONES, BILL is entered for a value of X$. These two
data items could be entered on separate lines. Notice that the
comma in the string value does not separate data items.
When each variable in the INPUT statement is assigned a value,
the program executes the NEXT statement (Iine30). At Iine30the
values of X$ and X are displayed on the screen.
The INPUT statement can also be used with the Program
Recorder to recover data. When the Program Recorder is used,
an OPEN statement must be executed before an INPUT
statement is encountered. The OPEN statement must include an
I/O channel number, the operation code for input (4), and the
device code ("C"). The third argument of the OPEN statement is
a special function code, and must be zero. If any of the
arguments of an OPEN statement are not integers, they are
rounded off.
Atari BASIC Reference Guide 131
The INPUT statement recovers data that was stored with the
PRINT statement.
EXAMPLE
10 DIM A$(100)
20 OPEN #1,4,0, "C"
30 INPUT #1, A$
40 PRINT A$
50 CLOSE #1
The previousexamplecontainsa program that readsand displays
one string value. Line 10 dimensions the variable A$. Line 20
opens I/O channel #1 for input from the Program Recorder.
When line 20 is executed, the tone sounds to remind the
operator to find the correct position on the tape, press PLAY on
the Program Recorder then press RETURN on the keyboard.
When line 30 is executed, one string value is read from the
cassette and assigned to the variable A$. Line 40 causes the value
of A$ to be displayed on the screen. Line 50 closes the I/O
channel.
Before an INPUT statement can be used with the Program
Recorder, the data must have been put on the cassette with a
PRINT statement.
The INPUT statement can also be used to recover data that was
saved on a disk. The INPUT statement has the same configuration
with the disk and cassette. The INPUT statement must includean
I/O channel number and variable names.
The OPEN statement for the I/O channel must include the
channel number and the operation code 4 (input) or 12 (input
and output). The third argument of the OPEN statement is zero,
and fourth argument is the device and filename.
132 User's Handbook to the Atari 400/800 Computers
EXAMPLES
OPEN #2, 4, 0, "D2:BUDGET.BAS"
OPEN #3, 12, 0, "D:NAMES"
If only one disk is in use, the device name is simple "D:". If 2 or
more disks are being used, the number of the disk must be
specified.
The INPUT statement can also be used with the keyboard. The
OPEN statement must include an I/O channel number,
operation code 4, special operation code 0, and the device "K".
EXAMPLE
10 DIM Y$(10)
20 OPEN #2, 4, 0, "K"
30 INPUT #2, X, Y$
40 PRINT X, Y$
50 CLOSE #2
The previous example contains a program that uses the
keyboard for input. Line 10 dimensions the variable Y$. Line 20
opens I/O channel #2 for input from the keyboard. When Iine30
is executed, the program waits for input. However, no prompt
symbol appears, and the data is not displayed when it is entered.
The first variable in the IN PUT statement is X. Since X is a numeric
variable, a numeric data item must be entered first. The second
variable in the INPUT statement is Y$. Since Y$ is a string variable,
a string data item must be entered next. A comma can be used to
separate the data items, or each data item can be followed by
RETURN.
Line 40 displays the values of the two variables, and line 50 closes
the I/O channel.
INT
The INT function returns the largest integer that is less than or
equal to the argument.
Atari BASIC Reference Guide 133
CONFIGURATION
X = INT (a)
EXAMPLES
PRINT INT (13.9)
13
PRINT INT (-4.7)
-5
LEN
The LEN function returns the number of characters in a string
value or variable, including spaces and punctuation.
CONFIGURATION
X = LEN (string)
EXAMPLE
10 DIM A$(20)
20 A$ = "JONES, BILL"
30 PRINT LEN(A$)
40 PRINT LEN("BILL JONES")
RUN
10
10
Line 10 dimensions the variable A$, and Iine20assigns A$a string
value. Line 30 displays the number of characters in the variable
A$. Line 40 displays the number of characters in the string "BILL
JONES".
LET (LE.)
The LET statement is optional. It is used to assign a value to a
variable.
134 User's Handbook to the Atari 400/800 Computers
CONFIGURATION
|LET| X$ = a a $
EXAMPLES
LET X = 250
X = Y + 25
LIST (L)
The LIST statement is used to display or record information in the
computer's memory.
CONFIGURATION
LIST [device:filespec,][LN][,LN]
The LIST statement can be used to save a program, or part of a
program, on a disk or cassette. The ENTER statement is the only
Atari BASIC statement that can recover a program saved with
LIST. The optional line numbers (LN) indicate the section of the
program that is to be saved. If no line numbers are specified, the
entire program will be saved. If only one line number is specifed,
only that line of the program is saved. If two line numbers are
specified, those two lines are saved along with all the code
between those line numbers. If either or both of the specified
line numbers do not appear, the section of the program between
those line numbers is saved.
A program is saved on a cassette tape with the statement LIST
"C". Before saving the program, the tape must be properly
positioned. When a LIST "C" statement is executed, the tone
sounds twice to remind the operator to press PLAY and RECORD
on the Program Recorder, followed by RETURN on the
keyboard.
DOS must be booted before a LIST statement can be used with a
disk. A program is saved on a disk with a statement of the form
LIST"device:filespec" followed by the appropriate line numbers
(if any).
Atari BASIC Reference Guide 135
EXAMPLE
10 DIM A$(10)
20 FOR A = 1 TO 100
30 PRINT A$, A A 2
40 IF A A 2>500THEN END
50 NEXT A
LIST"D:PROGR.BAS", 5,45
In the previous example, the LIST statement saves lines 10
through 40 on the disk. The line numbers that are specified (5
and 45) do not exist in the program, so the section of the program
with line numbers between those values is saved.
The device code "D: can be used only if one disk is in use. If more
than one disk is available, the number of the disk must also be
specified.
The LIST statement can also be used to display a program on the
monitor. The LIST command displays the entire program on the
screen unless the LIST statement is followed by line numbers.
If one line number follows the LIST statement, the line of the
program with that line number is displayed. If the program does
not have a line with the line number specified in the LIST
statement, the LIST statement has no results.
EXAMPLE
LIST 20
20 FOR A = 1 TO 100
READY
If two line numbers are specified, those two lines are displayed
along with all the code between those line numbers. If either or
both of the specified line numbers do not appear in the
program, the section of the program between those line
numbers is displayed.
The LI ST statement can also be used with a printer. The statement
136 User's Handbook to the Atari 400/800 Computers
LIST "?:" causes the program in the computer's memory to be
listed on the printer. The interface module and the printer must
both be turned on. Also, the printer must be online.
The computer's character set is slightly different from the
printer's, so certain characters appear differently when printed.
Also, the printer interprets some of the control characters as
commands. As a result, when control characters are printed, the
printer may have an unusual response. To avoid this problem, do
not use control characters within quotation marks. Instead, use
the CHR$ function to generate special characters.
EXAMPLE
PRINT "-*■" (escape, control - *)
PRINT CHR$(31) (preferred)
The computer can only accommodate 128 variables. If the limit is
exceeded, ERROR-4 occurs. The computer maintains a variable
name table with the names of all variables used since the NEW
command was executed. Asa result, the variable name table can
accumulate variable names that are no longer being used. The
LIST statement is the only Atari BASIC statement that saves a
program without saving the variable name table. As a result, the
LIST and ENTER statements can be used to eliminate unused
variables from the variable name table.
EXAMPLE
Save the program on cassette or disk using LIST.
Execute a NEW statement to clear the memory.
Put the program back into memory using ENTER.
LOAD (LP.)
The LOAD statement is used to recover programs that were
recorded with the SAVE statement.
CONFIGURATION
LOAD "devicerfilespec"
Atari BASIC Reference Guide 137
The LOAD statement is used with the Program Recorder or a
disk. The LOAD statement can only be used to recover programs
that were previously saved with a SAVE statement.
When a LOAD statement is executed, the computer's memory is
cleared before the new program is loaded. Also, the I/O
channels are closed (except 0),and the sound voices are shut off.
With the Program Recorder, the LOAD statement does not usea
filename. The cassette tape must be correctly positioned before
the LOAD statement is executed. Only the device name "C" is
necessary. When the LOAD "C" statement is executed, the tone
sounds once to remind the operator to press PLAY on the
Program Recorder, followed by RETURN on the keyboard.
With a disk, the LOAD statement must include a device name
along with a filename. If more than one disk is in use, thedevice
name must also include the number of the disk. If only one disk is
in use, the device name "D:" is sufficient.
EXAMPLE
LOAD "D2:GRADES"
LOCATE (LOC.)
The LOCATE statement is used to place the cursor at the
specified position, and assign the COLOR data at that point to
the specified numeric variable.
CONFIGURATION
LOCATE a, b, X
The first argument (a) indicates the column that the cursor is
moved to. The second argument (b) indicates the row. The third
argument is the numeric variable that is assigned the COLOR
data at the cursor position. A LOCATE statement can only be
used if a GRAPHICS statement has been executed.
The COLOR data in graphics mode corresponds to the
138 User's Handbook to the Atari 400/800 Computers
character graphics mode 1 and 2, the COLOR data indicates the
character and color register of a PLOT statement.
In graphics modes 3 through 8, the COLOR data actually
corresponds to the color register of a picture element.
EXAMPLE
10 GRAPHICS 3
20 COLOR 2
30 PLOT 0,0
40 DRAWTO 35,0
50 LOCATE 5, 0, X
60 PRINT X
The previous example consists of a program that uses the
LOCATE statement. Line 10 chooses graphics mode 3. Line 20
indicates that color register 2 is used in the PLOT and DRAWTO
statements. Since no SETCOLOR statement was executed, the
default color (green) is used. The PLOT statement at line 30
illuminates a green picture element at the upper left corner of
the screen. The DRAWTO statement at line 40 illuminates the
top row of the display in the same color. Line 50 is a LOCATE
statement that places thecursorat position 5,0. Since the line was
drawn from 0,0 to 35,0, the position 5,0 is an illuminated picture
element. The value of the color register at that position is 2. The
LOCATE statement assigns the color register value (2) to the
variable X. Line 60 is a PRINT statement that displays the value of
X.
The DRAWTO and XIO statements have separate memory
locations for the cursor position. As a result, a LOCATE statement
has no effect on the cursor position of a DRAWTO or XIO
statement.
When LOCATE is used to read a code from the screen, the cursor
will move one location to the right. If the cursor was on that last
column of a row when LOCATE was executed, the cursor may
attempt to advance to the first column of the next row resulting
in Error 141 (Cursor Out of Range).
Atari BASIC Reference Guide 139
LOCATE moves the cursor by altering the values stored in
memory address 84 (current cursor row number) and memory
addresses 85 and 86 (current cursor column number). The cursor
position change as a result of the execution of LOCATE will have
no effect on DRAWTO and XIO statements, as they use memory
addresses 90, 91, and 92 to determine the next cursor address.
LOG
The LOG function returns the natural logarithm of the
argument. The natural log function is undefined for arguments
less than or equal to zero.
CONFIGURATION
X = LOG(a)
EXAMPLES
PRINT LOG(2.71828183)
1
PRINT LOG (-1)
ERROR-3
A value error results from a zero or negative argument.
LPRINT (LP.)
The LPRINT statement sends a line of output to a printer.
CONFIGURATION
LPRINT [data] ' [data]...
The LPRINT statement can include numeric variable names and
string variable names, as well as string constants. String constants
must appear in quotation marks.
The items in an LPRINTstatement must be separated by a comma
140 User's Handbook to the Atari 400/800 Computers
or a semicolon. A semicolon causes the values to be printed on
the same line without any spaces. A comma causes the next item
to be printed at the next column stop location. A comma or
semicolon is optional at the end of a LPRINT statement. If a
semicolon is used at the end of a LPRINT statement, the next
output will be adjacent to the last output. If a comma is used at
the end of an LPRINT statement, the next output occurs at the
next column stop after the last output. If neither a comma nor a
semicolon is used at the end of an LPRINT statement, the next
output occurs on the next line.
When an LPRINT statement is executed, an error occurs if the
printer is not ready to operate.
The LPRINT statement uses I/O channel 7. If channel 7 is open
when an LPRINT statement is executed, an error will occur.
EXAMPLE
10 DIM A$(5)
20 A$ = "GREEN"
30 X = 25
40 LPRINT "INVENTORY: ";X,A$
In the previous example, LPRINT is used to print a string
constant, a string variable, and a numeric variable. The LPRINT
statement at line 40 prints the word INVENTORY followed by a
colon and a space. Any characters that appear in quotation
marks are reproduced as they appear. A semicolon separates the
items, so the value of X (25) follows the string.
A comma separates the variable names X and A$, so the value of
A$ is printed in the next display column.
NEW
The NEW command eliminates the current program in the
computer's memory. The NEW command erases all variables,
turns off all voices, and closes all I/O channels except channel 0.
Atari BASIC Reference Guide 141
CONFIGURATION
NEW
EXAMPLE
NEW
NEXT (N.)
The NEXT statement is used with a FOR statement to form a
repetitive section of a program.
CONFIGURATION
NEXTX
A FOR statement begins a loop, and a NEXT statement ends it.
The FOR statement sets an initial value and a final value for the
counter. The optional STEP statement specifies the amount that
the counter is increased or decreased each time the loop is
executed.
EXAMPLE
10 FOR I = 1 TO 10 STEP 2
20 PRINT I
30 NEXT I
In the previous example, the variable I is the counter. The initial
value of the counter is 1, and the final value is 10. The value of the
counter is incremented by 2 each time the loop is executed.
The section of the program between the FOR and NEXT
statements is repeated for each different value of the counter.
Each time the NEXT statement is executed, the value of the
counter is changed by the STEP argument value. The loop is
repeated for each value of thecounter. In the previousexample,
the loop is repeated 5 times, with the counter equal to 1, 3, 5, 7,
and 9. The initial value of thecounter (I) is 1, and it is increased by
2 each time the loop is executed because of the STEP 2 statement.
142 User's Handbook to the Atari 400/800 Computers
If no STEP statement is used, the counter value increases by 1
each time a NEXT statement is executed.
A FOR/NEXT loop can also have a decreasing counter. If the STEP
argument is negative, the value of the counter decreases each
time the loop is executed.
An increasing counter will repeat the loop until one more
increase would make the counter greater than the final value. A
decreasing counter will repeat the loop until one more decrease
would make the counter less than the final value.
When a loop has been completed, the statement after the NEXT
statement is executed.
NOT
NOT is a logical operator that returns the value 1 if its argument is
false. If its argument is true, the NOT statement returns the value
0.
CONFIGURATION
X = NOT EX
The following truth table describes the NOT operator.
A
NOT A
1
1
The computer represents the condition of true with the number
1. The false condition is represented by 0.
Numbers and expressions are considered true if they equal any
number other than 0. Only numbers that equal are false. The
following examples are true.
Atari BASIC Reference Guide 143
EXAMPLES
5>3
4
NOTO
NOT3>5
The following examples are false.
EXAMPLES
"DOG" = "CAT"
3>5
NOT 5
NOT 1
The NOT operator is generally used in IF/THEN statements.
EXAMPLE
If X>Y AND NOT Z THEN 250
NOTE (NO.)
The NOTE function returns the location of the file pointer for a
specified disk file. The NOTE function is not available in DOS
version 1.0.
CONFIGURATION
NOTE#a, X, Y
The NOTE function must specify a channel number (#a) that is
open for a disk file.
The second argument is a numeric variable that is assigned the
sector number of the file pointer. The third argument is a
numeric variable that is assigned the byte number of the file
pointer within the specified sector.
EXAMPLE
NOTE #2, SEC, BYT
144 User's Handbook to the Atari 400/800 Computers
ON
The ON statement is used to branch program control. When
used with a GOTO statement, the ON statement branches
program control to one of several lines. An ON statement is also
used with GOSUB to branch a program to one of several
subroutines.
configuration
3 ]ln[,ln].
ONX^-B
The argument of ON is the control expression. When a GOSUB
statement is used, the program proceeds to a subroutine. When
a GOTO statement is used, the program branches to a line
number.
The control expression determines to which line number the
program will proceed. If the control expression equals 1, the
program branches to the first line number after the GOTO or
GOSUB. If the control expression equals 2, the program
branches to the second line number after GOTO or GOSUB, etc.
If the control expression does not equal an integer, it is rounded.
If the control expression evaluates to or a numbergreaterthan
the number of choices of line numbers, the statement following
the ON statement is executed.
If the control expression is less than or greater than 255, an
error results.
EXAMPLE
10 X = 2
20 ON X GOTO 30, 40, 50
30 PRINT "FIRST": END
40 PRINT "SECOND":END
50 PRINT "THIRD":END
RUN
SECOND
Atari BASIC Reference Guide 145
The previous example consists of a program that uses an
ON/GOTO branch. At line 20, the ON/GOTO statement
branches to line 30, 40, or 50 depending on the value of X. Since X
is assigned the value 2, the ON/GOTO statement causes a
branch to the second line number. The second choice is line 40,
so the message SECOND is printed.
OPEN (O.)
The OPEN statement is used to open an input/output channel
for an input or output device. The computer cannot receive
input from or send output to a device unless an I/O channel has
been opened for that purpose.
CONFIGURATION
OPEN #a ; b, c, "device [:filespec]"
The first argument of an OPEN statement is the channel number.
The channels are numbered from through 7. Channel number
is always reserved for the editor. Channel number 6 is used for
graphics, and channel number 7 is used to save and load
programs. Channel number 7 is also used with the LPRINT
statement.
As a result, channels 1 through 5 are available for use with BASIC
programs. Channels 6 and 7 are available only on a limited basis
for use with BASIC programs. Channel 6 is available if no
graphics are used. Channel 7 is available unless programs are
being loaded or saved. Also, channel 7 is unavailable if an
LPRINT statement is executed.
The second argument indicates the operation of the
input/output device. In general, the second argument is 4 if the
computer is accepting information (input). The second
argument is generally 8 if the computer is sending information
(output) to a device. Table 5-1 contains a complete list of I/O
operations with their associated devices and operation numbers.
146 User's Handbook to the Atari 400/800 Computers
Table 5-1. I/O Operations
Device
Operation
Number
Operation Type
Program Recorder
4
8
input
output
Keyboard
4
input
Printer
8
output
Editor
8
12
13
output:screen
input:keyboard
outputrscreen
input:screen
output:screen
Disk
4
6
8
9
12
input
read disk directory
output, new file
output, append
input and output, update
Interface
5
8
9
13
.-_ -
concurrent input
block output
concurrent output
concurrent input and output
The third argument of an OPEN statement indicates a special
operation. The special operation code is usually 0. Generally, the
third argument is only used when opening the screen display for
a graphics mode.
If any of the first three arguments of an OPEN statement are not
integers, they are rounded off.
The fourth argument of an OPEN statement is the device name.
The device names used by Atari computers are listed below. The
device name and file specification (if present) must be enclosed
in quotation marks.
Atari BASIC Reference Guide 147
Program Recorder
C
Screen Editor
E.
Keyboard
K
Printer
P
Display
S:
Disk
D
Program Recorder
An I/O channel can be opened for the Program Recorder for
either input or output, but not both at the same time. When the
OPEN statement is executed, the tape must be at the correct
location before proceding.
When an OPEN statement is executed for output to the Program
Recorder, the tone sounds twice. This is a reminder for the
operator to press Play and Record on the Program Recorder,
followed by Return on the keyboard. For input, the tone sounds
once to remind the operator to press Play on the Program
Recorder, followed by Return on the keyboard.
The third argument of an OPEN statement for the Program
Recorder can be either or 128. The files are recorded with
shorter gaps between the records when the third argument is
128.
When an OPEN statement is executed, and the correct levers on
the Program Recorder are pressed, the Program Recorder
begins operating as soon as the Return key on the keyboard is
pressed. The tape keeps moving until a set of data (128 bytes) is
accumulated for output. While data is being accumulated,
nothing is recorded on the tape. Asa result, if a long delay occurs
from the period when the OPEN statement is executed to when
the information is recorded, a long gap appears on the tape.
When a long section of blank tape (30 sec. or more) is
encountered during input, a Device Timeout error occurs. To
avoid these errors, the I/O channel should be closed whenever a
delay in the output procedure occurs.
148 User's Handbook to the Atari 400/800 Computers
Keyboard
The OPEN statement for the keyboard can be for input only.
When the keyboard is used for input, the question mark does
not appear as a prompt for an INPUT statement. Also, the
response to an INPUT statement does not appear on the display.
The third argument of an OPEN statement for the keyboard is
ignored.
EXAMPLE
10 DIM A$(1)
20 OPEN #2, 4, 0, "K:"
30 GRAPHICS 3 + 16
40 INPUT #2, A$
50 PRINT
60 END
The previous example contains a program that maintains a
graphics display until input is received from the keyboard. Line
10 dimensions the string variable A$. Line 20opensthe keyboard
for input. Line 30 selects graphics mode 19, which is the same as
graphics mode 3, but without a text window.
In order to maintain a full screen graphics display, the program
must pause, but not end. When a character is displayed, the
display returns to graphics mode 0.
When the INPUT statement is executed at line 40, the program
waits for input, but does not ruin the display by printing the
prompt (?) or the response. As a result, the display is preserved
until the operator enters a suitable input for A$. The easiest
response to the INPUT statement is the Return key.
Disk
An I/O channel can be opened for a disk for any of the I/O
operations listed in Table 5-1. When an OPEN statement for the
disk is executed, DOS must have been booted and ready to
operate.
An OPEN statement for a disk file must in Icude the filename and
Atari BASIC Reference Guide 149
optional filename extension. The filename extension must be
separated from the filename by a period.
The following examples are correct OPEN statements for a disk.
EXAMPLE
OPEN #1, 4, 0, "D2:GRADES.BAS"
OPEN #3, 12, 0, "D:JONES"
Printer
An I/O channel for the printer can be for output only. The
printer must be turned on before the OPEN statement is
executed. If the printer is used with the Atari 850 interface, this
also must be ready to operate. The printer must be in the Online
mode if it has Local/Online switch.
The third argument of an OPEN statement for the printer is
generally 0. However, the Atari 820 printer outputs sideways
characters if the third argument is 83.
Editor
An OPEN statement for the editor allows the screen and
keyboard to be used for input and output. When an OPEN
statement is executed for the editor, the display resumes
graphics mode 0, the screen is cleared, the cursor is reset, and
the color registers are set to the default values.
The editor can be used in one of three modes. The mode is
determined by the second argument of the OPEN statement
(Table 5-1). The display is always used for output, but the display
or the keyboard can be used for input.
The third argument of an OPEN statement for the editor is
ignored. Even though this value has no effect, it must always be
included in the OPEN statement.
150 User's Handbook to the Atari 400/800 Computers
EXAMPLE
10 OPEN #1, 13, 0, "E:"
20 T = 3.14
30 PRINT T
40 POSITION 0,0
50 INPUT #1, X
60 PRINT X
70 END
The previous example contains a program that uses the display
screen as an input device. Line 10 opens I/O channel number
one for the editor (device "E:"). The second argument of the
OPEN statement (13) indicates that the display is used for input
and output. The second line of the program assigns the value
3.14 to the variable T. Line 30 causes the value of T to be displayed
on the screen. Since the OPEN statement clears the screen and
resets the cursor, the value 3.14 is displayed at the upper left
hand corner of the screen.
The POSITION statement at line 40 returns the cursor to the
upper left hand corner of the screen. The INPUT statement at
line 50 chooses the device on I/O channel 1. As a result, the
screen is used to input a value for the variable X.
When an INPUT statement is used with the screen, the value that
follows the cursor is used for input. Since the value 3.14 appears
at the top of the screen, and the cursor is also at the top of the
screen, the value 3.14 is assigned to X. Line 60 displays the value
of the variable X.
The output of this program is the value 3.14 displayed twice. The
number is repeated because it is printed at lines 30 and 60.
Screen
The OPEN statement for the screen (device "S:") is used to
choose a graphics mode. The third argument of the OPEN
statement indicates the graphics mode (0 through 8). The second
argument indicates if the screen is used for input or output, or
both. Also, the second argument determines if the display has a
text window and if the display is cleared when the OPEN
statement is executed.
Atari BA5IC Reference Guide 151
Table 5-2. Screen I/O Operations
OPERATION
NUMBER
OUTPUT
INPUT
TEXT
WINDOW
CLEAR
SCREEN
8
12
24
28
40
44
56
60
NOTE: The screen is always clear in graphics mode 0.
Graphics mode has no separate text window.
When the screen is used with an OPEN statement instead of a
GRAPHICS statement, the PLOT and DRAWTO statements
cannot be used. Input and output is performed with PRINT, PUT,
and GET statements. Each of these statements require an I/O
channel number that corresponds to the OPEN statement
channel number.
EXAMPLE
10 GRAPHICS 8
20 COLOR 1
30 PLOT 0,0
40 DRAWTO 10,10
50 OPEN #1, 60, 8, "S:"
60 POSITION 5,5
70 GET#1, X
80 PRINT X
90 END
The previous example contains a program that uses the screen as
an input device. Line 10 has a GRAPHICS statement that indicates
graphics mode 8. Line 20 chooses color number 1. Lines 30 and 40
draw a small diagonal line in the upper left of the display.
152 User's Handbook to the Atari 400/800 Computers
At line 50, the display is opened as an I/O device. The first
argument of the OPEN statement indicates the I/O channel
number. The second argument indicates that the screen is used
for input and output. Also, a text window is present, and the
screen isnotcleared (Table5-2). The third argument of theOPEN
statement indicates graphics mode 8.
At line 60, the cursor is positioned at the location of 5,5. The GET
statement at line 70 assigns the color number at the cursor
postion to the variable X. Since the cursor is at location 5,5, the
color number at that location is 1 (5,5 is one of the points on the
line between 0,0 and 10,10). The PRINT statement at line 80
displays the value of the variable X in the display window.
Atari 850 Interface Module
An OPEN statement for a serial port of an Atari 850 Interface
module requires the device name "R:". The number of the port
is also necessary for ports 2 through 4. The first argument of the
OPEN statement is the I/O channel. The second argument
determines the I/O operation, as listed in Table 5-1. The third
argument is ignored. Although the third argument has no effect,
it must appear in the OPEN statement.
The interface module must be ready to operate when the OPEN
statement is executed. It will not operate unless it was turned on
before the computer console was turned on. Also, the interface
module may not operate properly until the appropriate XIO
statements have been executed.
The following examples are correct OPEN statements for the
interface module.
EXAMPLES
OPEN #1, 5, 0, "R2
OPEN #2, 13, 0, "R
OPEN #4, 8, 0, "R4
Atari BASIC Reference Guide 153
OR
The OR statement is a logical operator that returns the value 1 if
either one of its arguments are true. An OR statement returns
the value only if both of its arguments are false.
CONFIGURATION
EX OR EX
The conditions of true and false are represented by the values 1
and respectively. The results of the OR operation are
represented by the following truth table.
A
B
A ORB
1
1
1
1
1
1
1
An OR statement can have either relational or algebraic
expressions for arguments. Any algebraic expression that does
not equal zero is true. An expression that equals zero is
considered false.
EXAMPLES
5 (true)
3-7 (true)
"DOG" = "CAT" (false)
8<2 (false)
In the previous examples, 5 is considered true because it does
not equal zero. The expression 3-7 is also true because it does not
evaluate to zero. The relational expression "DOG" = "CAT" is
false because the string constants are not equal. The expression 8
<2 is also false.
154 User's Handbook to the Atari 400/800 Computers
EXAMPLE
10 X = 5
20 Y = 10
30 IF X = 10 OR Y THEN PRINT Y
40 END
RUN
10
The previous example consists of a program that uses an OR
statement within an IF/THEN statement. LinelOsetsXequal to 5.
Line 20 sets Y equal to 10. Line 30 displays the value of Y if either
(or both) of the arguments of the OR statement are true. The first
argument of the OR statement is the relational expression X = 10.
Since X is set equal to 5 in line 10, this expression is false. The
second argument of the OR statement is the algebraic
expression Y. The expression (Y) is considered false only when it
equals zero. Since Y is set equal to 10 at line 20, the expression is
considered true.
As a result, the OR statement is true because one of the
arguments is true. The value of Y is displayed because the
condition of the IF/THEN statement is true.
PADDLE
The PADDLE function returns an integer between 1 and 228 that
depends on the rotation of a particular paddle.
CONFIGURATION
X = PADDLE (a)
A total of 8 paddle game controllers can be used at one time. The
value of the argument (a) indicates the number of the paddle. If
the argument of the PADDLE statement is not an integer, it is
rounded off. The paddles are numbered through 7. If the
PADDLE statement has an argument greater than 7, the results
are unpredictable. If a paddle is not present when a PADDLE
statement is executed, the value 228 is returned.
Atari BASIC Reference Guide 155
The paddle controllers are used only in pairs. A pair of
controllers is plugged into one of the controller jacks on the
front of the computer. The first jack accepts paddles and 1. The
second jack accepts paddles 2 and 3, etc.
If a paddle is rotated fully clockwise, the value 1 is returned. The
value increases as the paddle is rotated counter-clockwise. The
maximum value returned is 228.
EXAMPLE
10 IF PADDLE (1)=150 THEN END
20 GOTO 10
The previous example consists of a program that executes line 10
repeatedly until the paddle is rotated more than halfway
counter-clockwise. Since PADDLE (1) specified, the paddles
must be plugged into controller jack 1.
PEEK
The PEEK function is used to recover the value in a memory
location.
CONFIGURATION
X = PEEK (a)
A memory location contains an integer value between Oand 255.
The argument of a PEEK statement refers to the memory
location. A value error occurs if the argument is negative or
greater than 65535. If the argument (a) is not an integer, it is
rounded off.
Many memory locations are of general interest. The contents of
a memory location can be changed with a POKE statement.
Appendix E contains information about commonly used
memory locations.
EXAMPLE
PRINT PEEK (83)
39
156 User's Handbook to the Atari 400/800 Computers
The previous example displays the current value for the right
margin of the screen. The default value is 39.
PLOT (PL)
The PLOT statement is used to display a character or picture
element on the display.
CONFIGURATION
PLOT a,b
The arguments of a PLOT statement determine the position on
the screen where the character or picture element appears. The
first argument (a) indicates the column, and the second
argument (b) indicates the row. The graphics mode specified
determines the number of rows and columns of the display. If
either of the arguments is not an integer, it is rounded off. If
either argument is negative or greater than the dimension of the
screen an error results.
In graphics mode 0, the COLOR statement indicates the
character that will appear at the next PLOT location. However,
the COLOR statement has nothing to do with the color of the
character. Table 9-7 indicates the COLOR value for each
character.
In graphics modes 1 and 2, the COLOR statement indicates the
character and location register used in the next PLOT location.
Table 9-4 indicates the COLOR value for each character in each
color register. In graphics modes 1 and 2, color registers are
available for each character. As a result, each character can be
displayed in any of 4 colors.
In graphics modes 3 through 8, the PLOT statement illuminatesa
picture element at the screen position indicated by the
arguments of the PLOT statement. The dimensions of the display
depend on the graphics mode. The number of possible colors
also depends on the graphics mode.
Atari BASIC Reference Guide 157
EXAMPLE
10 GRAPHICS 3
20 COLOR 2
30 FOR I = TO 35 STEP 5
40 PLOT 1,0
50 NEXT I
The previous example contains a program that uses a PLOT
statement. Line 10 indicates graphics mode 3. Line 20 chooses the
color register 2. Since no SETCOLOR statement was executed,
color register 2 defaults to green. Line 30 begins a FOR/NEXT
loop that is executed 8 times. The value of the counter (I) is set to
equal 0, 5, 10, 15. ..35. As a result, line 40 causes green picture
elements to appear evenly spaced across the top of the display.
The PLOT statement indicates positions (0,0), (5,0), (10,0). ..(35,0).
The first argument is the column, and the second argument is the
row. The second value indicates the top line (zero row) of the
display.
POINT (P.)
The POINT statement is used only in disk operations to move the
file pointer to a given location.
CONFIGURATION
POINT #a, b, c
The first argument of a POINT statement indicates an I/O
channel. The channel must be open to a disk for input, update,
or append. The second argument is the sector value. The sector
value must lie within the limits of the file. The third argument is
the number of the byte within the sector. The third argument
must be between and 125. If any of the arguments are not
integers, they are rounded off.
The POINT command is not valid in version 1.0 of the disk
operating system.
158 User's Handbook to the Atari 400/800 Computers
EXAMPLE
POINT #3, SECT, BYTE
In the preceding example, the file pointer for the disk file
opened through channel #3 is moved to the sector specified by
trie variable, SECT, and byte within that sector specified by the
variable, BYTE.
POKE (POK.)
The POKE statement is used to store one byte of information in a
particular memory location.
CONFIGURATION
POKE a, b
The first argument of a POKE statement is the memory location.
If a POKE statement specifies a memory location that does not
exist, the POKE statement has no effect. Also, if a POKE
statement specifies a memory location that is part of the ROM,
the POKE statement has no effect.
The second argument of a POKE statement is the value that is to
be stored at the specified memory location. The value of the
second argument represents one byte. As a result, the value must
be an integer between and 255.
If either of the arguments of a POKE statement is not an integer,
it is rounded off. A value error occurs if the memory location
specified is greater than 65535 or the value of the second
argument exceeds 255. A value error also results if either of these
arguments are negative.
If the POKE statement is not used carefully, it can seriously
disrupt the operation of the computer.
Appendix E contains information regarding commonly used
memory locations.
Atari BASIC Reference Guide 159
EXAMPLE
POKE 83,20
The previous example consists of a statement that changes the
right margin of the screen to column 20. The value of the right
margin is stored in memory location 83.
POP
The POP statement causes a program to ignore the GOSUB or
ON/GOSUB statement that was executed last.
CONFIGURATION
POP
In effect, a GOSUB or ON/GOSUB statement is converted to a
GOTO or ON/GOTO statement when POP is executed. The
program "forgets" that it is in a subroutine. As a result, when a
POP statement is executed, the next RETURN statement
branches the program control to the line after the GOSUB
statement before the previous GOSUB statement. In other
words, the program "forgets" where the subroutine was called
from, so it returns to a previous GOSUB statement.
A POP statement is used, in general, to exit a subroutine.
EXAMPLE
10 X = 5
20 Y = 10
30 GOSUB 100
40 END
100 PRINT X
110 IF X>0 THEN POP:GOTO 130
120 RETURN
130 PRINT Y
140 END
RUN
5
10
160 User's Handbook to the Atari 400/800 Computers
The previous example contains a program that uses a POP
statement to exit a subroutine. At line 10, X is assigned the value
5. At line 20, Y is assigned the value 10. At line 30, the subroutine
at line 100 is called.
At line 100, the value of X is displayed. Line 110 is an IF/THEN
statement that tests the condition X>0. Since the value of X is
greater than zero, the condition is true. As a result, the POP
statement is executed, and the program control branches to line
130. At line 130, the value of Y is displayed.
Since the POP statement was executed, the program is no longer
in the subroutine. If another RETURN statement isexecuted, the
program will not return to line 30, where the subroutine was
called. The program will return to the line of the previous
GOSUB statement. Since there is no other GOSUB statement in
this program, a RETURN statement would cause an error.
A POP statement can also be used to make the program ignore
the previous FOR statement. When a POP statement is executed
within a FOR/NEXT loop, the loop will not be repeated.
However, an erroroccurs if a NEXT statement isexecuted forthat
loop.
POSITION (POS.)
The POSITION statement moves the cursor to the specified
column and row.
CONFIGURATION
POSITION a, b
The first argument of the POSITION statement determines the
column, and the second argument determines the row. The
cursor does not actually move when the POSITION statement is
executed. The cursor takes on the new position when the next
PUT, GET, PRINT, INPUT, or LOCATE statement is executed.
If a POSITION statement specifies a location that is outside the
range of the display, no error occurs until another statement that
Atari BASIC Reference Guide 161
uses the display is executed.
A POSITION statement does not affect the DRAWTO, PLOT, or
XIO functions. These operations maintain a separate cursor
location.
EXAMPLE
10 GRAPHICS
20 POSITION 5, 4
30 PRINT EXP(1)
The previous example contains a program that uses a POSITION
statement. The GRAPHICS statement causes the display to be
cleared. Line 20 moves the cursor to column number 5 and row
number 4. Line 30 prints the output on the screen at the position
of the cursor. As a result, the value 2.71828179 is displayed four
lines from the top of the display and 5 columns from the left
margin.
PRINT (PR. or ?)
The PRINT statement is generally used to display characters on
the screen, but a PRINT statement can be used to output
characters to any output device.
CONFIGURATION
PRINT[#a;] [expression][ ? ]...
The PRINT statement can include numeric variable names and
string variable names, as well as string and numeric
constants. String constants must appear in quotation marks.
Items within a PRINT statement must be separated by a comma
or a semicolon. A semicolon causes the values to be printed on
the same line, without any spaces between items. A comma
causes the next item to be printed at the next column stop
location.
162 User's Handbook to the Atari 400/800 Computers
If a semicolon is used at the end of a PRINT statement, the next
PRINT statement output will be adjacent to the last output. If a
comma is used at the end of a PRINT statement, the next output
occurs at the next column stop after the last output. If neither a
comma nor a semicolon is used at the end of a PRINT statement,
the next output occurs on the next line.
Column stops occur at intervals of 10 spaces. However, if the last
character that was printed is within two spaces of the next
column stop, that column stop will be ignored. As a result, items
in a PRINT statement that are separated by commas will have at
least two spaces between them.
EXAMPLE
10 DIM A$(15)
20 A$ = "THOMAS R SMITH"
30 X = 27
40 PRINT "NAME:"; A$, "AGE:"; X
50 END
The previous example contains a program that uses a PRINT
statement. At line 10, the variable A$ is dimensioned. At line 20,
the variable A$ is assigned the string value "THOMAS R SMITH".
At line 30, the variable X is assigned the value 27.
Line 40 contains a PRINT statement. The string constant
"NAME:" is printed first, followed immediately by the value of
the variable A$. Since a comma follows the variable A$, the string
constant "AGE:" is printed in the next available column.
However, the last character was printed in column 19, so the
column stop at column 20 is ignored. As a result, the string
constant "AGE:" and the value of the variable X are displayed in
the last column.
A PRINT statement requires an I/O channel number for any
output device other than the display. The I/O channel must be
open for an appropriate output operation.
Atari BASIC Reference Guide 163
Program Recorder
A PRINT statement that is used with the Program Recorder is
generally used to store data that will be recovered with an INPUT
statement.
If the OPEN statement for the Program Recorder specifies short
gaps between the records (special operation code 128), the tape
does not stop moving. The data is not recorded correctly if the
program does not supply data fast enough to keep up with the
tape.
EXAMPLE
10 OPEN #1, 8, 0, "C:"
20 FOR I = 1 TO 100
30 X = INT (RND (9) * 100)
40 PRINT #1,X
50 NEXT I
60 CLOSE #1
70 END
The previous example contains a program that records 100
random numbers on tape. Line 10 opens I/O channel number 1
for output to the Program Recorder. At line 20, a FOR/NEXT loop
is set up to be repeated 100 times. Line 30 assigns a random
number between and 99 to the variable X. At line 40, the value
of X is printed on tape, using the Program Recorder. Line 50 is the
NEXT statement that completes the FOR/NEXT loop. Line 60
closes the I/O channel, and line 70 ends the program.
Disk
A PRINT statement that is used with a disk is generally used to
store data that will be recovered with an INPUT statement.
The format for using a PRINT statement with a disk is the same as
with the Program Recorder. The appropriate OPEN statement
must precede the PRINT statement. The I/O channel must be
open for update, append, or output to the disk file.
164 User's Handbook to the Atari 400/800 Computers
Printer
A PRINT statement for a printer also requires a previous OPEN
statement. Some of the characters may not be printed exactly as
they are displayed on thescreen. Different typesof printers have
different character sets, so the actual results depend on the type
of printer being used.
Display
The use of a PRINT statement in the graphics mode is
complicated but not difficult. In graphics modes 1 and 2, the
PRINT statement displays characters on the screen. In graphics
modes 3 through 8, the PRINT statement displays a picture
element on the screen.
A PRINT statement can be used in a graphics mode if an OPEN
statement has been executed for output to device "S:". Also, a
PRINT statement can be used in a graphics mode if a GRAPHICS
statement has been executed.
The PRINT statement must include an I/O channel number if a
corresponding OPEN statement has been executed. The PRINT
statement must include I/O channel number 6 if a GRAPHICS
statement was executed. When a PRINT statement is used with
graphics, the I/O channel number should be followed by a
semicolon instead of a comma.
In graphics modes 1 and 2, the characters are displayed as they
appear in Table 9-4. There are two sets of characters available by
executing appropriate POKE statements. Each of these
characters can be displayed in any one of four colors.
In Table 9-4, each character has four numbers associated with it.
These four numbers correspond to the four color registers. In
order to display one of the characters from Table 9-4 with a
PRINT statement, the PRINT statement must include the
character from Table 9-7 that has the same number as the desired
character from Table 9-4.
Atari BASIC Reference Guide 165
EXAMPLE
10 GRAPHICS 2
20 PRINT #6; "ATARI"
30 PRINT #6; "atari"
40 END
The previous example contains a program that uses two PRINT
statement in graphics mode 2. At line 20, the PRINT statement
indicates I/O channel number 6, which is used for graphics. To
determine which characters are to be printed, it is necessary to
consult Table 9-7 first. The upper case letters "ATARI" are
represented on Table 9-7 by the values 65, 84, 65, 82, and 73. The
characters that correspond to these values, on Table 9-4, are the
characters that will be displayed. These values indicate the
characters "ATARI" in color register from Table 9-4.
Similarly, the second PRINT statement has the lower case letters
"atari". These characters have the values 97, 116, 97,114, and 105.
On Table 9-4, these values correspond to the upper case letters
"ATARI" in color register 1. As a result of this program, the
message "ATARI" appears in orange and in light green.
In graphics modes 3 through 8, a PRINT statement illuminates
one picture element for each character in the PRINT statement.
The color of the picture element is derived from the ASCII code
of the character. In the four-color graphics modes (3, 5, and 7),
the ASCII codes is reduced modulo 4 to a number from to 3.
This value corresponds to the color value of the picture element.
In the two-color graphics modes (4, 6, and 8), the ASCII code is
reduced modulo 2 to indicate color value or 1.
Atari 850 Interface
A PRINT statement for a serial port of an Atari 850 Interface
module must be preceded by an appropriate OPEN statement.
Also, the interface module must be ready to operate. The
interface module will not operate unless it was turned on before
the computer console was turned on.
166 User's Handbook to the Atari 400/800 Computers
PTRIG
The PTRIG function returns the value of if thespecified paddle
controller button is depressed. A 1 is returned if the button is
released.
CONFIGURATION
X = PTRIG(a)
The value of the argument (a) indicates the number of the
paddle. A pair of controllers can be plugged into each of the
controller jacks on the computer. The first jack accepts paddles
and 1. The second jack accepts paddles 2 and 3, etc. A total of 8
paddle controllers can be used at one time.
EXAMPLE
IF PTRIG(3) = 0THEN END
The statement in the preceding exampleendsthe program if the
button on paddle 3 is being pressed.
PUT (PU.)
The PUT statement is used to send one byte to an output device.
One byte represents an integer between and 255.
CONFIGURATION
PUT #a, b
The first argument of a PUT statement is the I/O channel
number. The second argument is the value that is sent to an
output device. If either of the arguments are not integers, they
are rounded off.
An OPEN statement must precede the PUT statement except
when the PUT statement is used with graphics displays. The first
argument of the PUT statement must correspond to the I/O
Atari BASIC Reference Guide 167
channel number in the OPEN statement. When a PUT statement
is used for the display following a GRAPHICS statement, the I/O
channel number must be 6.
The I/O channel must be open for output to an appropriate
output device.
The second argument can be any non-negative value, but the
value that is sent to the output device will always be an integer
between and 255. Larger values are reduced modulo 256.
With the Program Recorder, an OPEN statement is needed to
open an I/O channel for device "C:". When the Program
Recorder is used for short gaps between records, the tape keeps
moving until the I/O channel is closed. As a result, the program
must keep up with the tape or the information will not be
recorded properly.
EXAMPLE
10 OPEN #1, 8, 0, "C:"
20 FOR I = 1 TO 100
30 X = INT(RND(9) * 100)
40 PUT#1, X
50 NEXT I
60 END
The previous example contains a program that records 100
random numbers. Line 10 is an OPEN statement that opens I/O
channel number 1 for output to the Program Recorder. Line 20 is
a FOR statement that begins a FOR/NEXT loop that is repeated
100 times. Line 30 sets X equal to a random integer between Oand
100.
Line 40 contains a PUT statement that sends the value of the
variable X to the output device on I/O channel number 1. Since
the I/O channel is open for output to the Program Recorder, the
values of the variable X are recorded on the cassette tape. When
the FOR/NEXT loop has been executed 100 times, the END
statement at line 60 closes the I/O channel and ends the
program.
168 User's Handbook to the Atari 400/800 Computers
The same format of the PUT statement is used with the Atari disk
drive. The I/O channel for the disk file must be opened for an
appropriate output option. Only a GET statement can be used to
recover the values that were recorded with a PUT statement.
When the display is used as an output device (S: or E:), a PUT
statement is used to place one character or illuminate one
picture element on the screen. The PUT statement causes the
output to appear at the current position of the cursor.
In the text modes, the value of the PUT statement corresponds to
the COLOR value of each character (Tables 9-4 and 9-7). As a
result, a POSITION and PUT statement have the same result as a
COLOR and PLOT statement.
EXAMPLE
10 GRAPHICS 2
20 POSITION 9,3
30 PUT #6,65
The previous example contains a program that uses a PUT
statement in graphics mode 2. Line 20 positions the cursor near
the center of the screen. The graphics modes always use I/O
channel number 6. As a result, the PUT statement at Line 30
displays the character "A" at the current cursor position. The
characters that correspond to the PUT statement values are listed
in Tables 9-4 and 9-7.
When a PUT statement sends the value 125 to the screen, the
display is cleared. Also, when the value 155 is sent to the screen,
the cursor returns to the beginning of the next line.
Atari BASIC Reference Guide 169
In the four-color graphics modes (3, 5, and 7), the value that a
PUT statement sends to the screen is reduced modulo 4 to a
value between and 3. The PUT statement illuminates the
picture element at the current position of the cursor.
The color of the picture element is determined by the value
between and 3 in the same way that a COLOR statement value
determines the color.
In the two-color graphics modes (4, 6, and 8), the value of the
PUT statement is reduced modulo 2 to the numbers or 1. The
color of the picture element is determined by the values Oand 1
in the same way that a COLOR statement determines the color.
A PUTstatement can also be used to send output to a printer. The
printer must be ready to operate when the corresponding OPEN
statement is executed.
PUT can also be used to send data to an open RS-232 serial port
on the Atari 850 Interface Module.
RAP
The RAD statement causes the trigonometric functions to be
performed in radians.
CONFIGURATION
RAD
EXAMPLE
RAD
The trigonometric functions are performed in radians until a
DEG statement is executed. Also, radians are used following a
NEW or RUN statement or following a System Reset.
170 User's Handbook to the Atari 400/800 Computers
READ (REA.)
A READ statement is used to assign values to variables. The values
are taken individually from DATA statements in the order they
appear in the program.
CONFIGURATION
READ
Data items are assigned to variables in the order in which they
appear in the program unless a RESTORE statement has been
executed.
The type of variable in the READ statement must correspond to
the type specified in DATA. A numeric variable can only be
assigned a numeric value. However, a string variable can accept
any type of characters or none at all.
String variables must be correctly dimensioned before the READ
statement for that variable is executed.
A program must include at least as many data items as the
number of variables in its READ statements unless a RESTORE
statement is executed.
EXAMPLE
10 DIM X$(10)
20 READ X,X$
30 PRINT X$,X
40 END
50 DATA 12, JONES
RUN
JONES 12
The preceding example contains a program that has a READ
statement. First, the string variable X$ is dimensioned. Next, at
line 20, the variables X and X$ are assigned the values from the
DATA statement at line 50. At line 30, the values of the two
variables are displayed.
Atari BASIC Reference Guide 171
A READ statement can accept data from a DATA statement that
appears anywhere in a program. A DATA statement does not
have to precede the READ statement in order to be effective.
REM (R. or .)
A REM statement is used to insert comments in a program. The
REM statement is ignored by the Atari BASIC interpreter.
CONFIGURATION
REM remarks
EXAMPLE
REM INPUT ROUTINE
Any statements that follow a REM statement, on the same line,
are also ignored by the computer. Asa result, a REM statement is
generally used on its own line or at the end of a multiple
statement line.
RESTORE (RES.)
A RESTORE statement is used to move the data pointer.
CONFIGURATION
RESTORE [LN]
The data in a program is read in order, starting with the first
DATA statement item. In order to reread a section of data, a
RESTORE statement is necessary.
When a RESTORE statement is executed without an argument,
the next READ statement will assign to its first variable the first
data value that appears in the program.
When a RESTORE statement is executed with an argument, the
next READ statement will assign to its first variable the first data
value that appears at the line number specified by the argument.
172 User's Handbook to the Atari 400/800 Computers
EXAMPLE
RESTORE 100
The previous example contains a statement that moves the data
pointer to the DATA statement at line 100. If line 100 is not a
DATA statement, the data pointer is moved to the next DATA
statement after line 100.
RETURN (RET.)
A RETURN statement is used to branch a program back to the
line where the last subroutine was called.
CONFIGURATION
RETURN
A subroutine is called with a GOSUB or ON/GOSUB statement.
When the subroutine has been completed, a RETURN statement
causes the program control to return to the statement following
the most recently executed GOSUB or ON/GOSUB statement.
EXAMPLE
RETURN
When a POP statement is executed before a RETURN statement,
the most recent GOSUB statement is ignored, and the program
control is branched to the next most recent GOSUB statement.
RND
The RND function is used to generate random numbers.
CONFIGURATION
X = RND(a)
The argument of a RND statement has no effect on the results,
but it is necessary. The value of the random number is less than 1
and greater than or equal to zero.
Atari BASIC Reference Guide 173
EXAMPLE
X = INT(RND(9) * 100)
The previous example contains a statement that generates
random integers between and 99 inclusive.
RUN (RU.)
The RUN statement is used to execute the program that is
currently in the computer's memory. A RUN statement is also
used to load and execute a program from an input device.
CONFIGURATION
RUN ["device:filespec"]
A RUN statement closes the I/O channels and turns off the
sound voices before executing or loading the program.
When a RUN statement is used with an input device, the
contents of the computer's memory are erased before the
program is loaded. Only BASIC programs that were recorded
with the SAVE statement can be loaded and executed with a RUN
statement.
The Program Recorder is activated with a RUN "C:" statement.
The tone sounds once to remind the operator to position the
tape and press the Play lever on the Program Recorder followed
by Return on the computer's keyboard.
A RUN statement can load and execute a program from a disk file
if the disk operating system has been booted. An error results if
the specified file does not exist.
EXAMPLES
RUN "C:"
RUN "D2:JONES.BAS"
174 User's Handbook to the Atari 400/800 Computers
SAVE
The SAVE command is used to send a BASIC program in RAM to
an output device.
CONFIGURATION
SAVE device
where device is a device name such as the program recorder (C:)
or disk drive (D:). In the case of the disk drive, a filename maybe
specified with the device name. The program will be saved
under the filename specified.
Files saved via SAVE are transferred in tokenized format. These
files can only be subsequently loaded using LOAD or RUN.
CLOAD and ENTER will not load a program saved with SAVE.
SAVE With The Program Recorder
The SAVE C: command is used to transfer a program to the
program recorder. When SAVE C: is executed, the Atari's
speaker will sound twice to indicate that the tape is to be
positioned correctly to receive the file. Once the tape has been
positioned, press the Record and Play buttons on the recorder.
Then, press any key on the Atari's keyboard. The program will
then be transferred from RAM to the program recorder.
SAVE With The Disk Drive
Before SAVE can be used to transfer a program to the disk drive,
DOS must have first been booted. An error will result if an
attempt is made to execute SAVE when DOS has not been
booted. If a file with the same filename as the file specified with
SAVE already exists on the diskette to which the program is being
transferred, the file being transferred will replace the file on
diskette with the same name.
Atari BASIC Reference Guide 175
SETCOLOR (SE.)
The SETCOLOR statement is used to assign a color and
luminance value to the color register specified.
CONFIGURATION
SETCOLOR register #, color, luminance
The color register must range from to 4 inclusive. The color
must range from to 15 inclusive. These values and their
corresponding colors are listed in Table 9-3. The luminance can
range from (darkest) to 14 (brightest).
Each of the 5 color registers has a default color and luminance
value. These default values are listed in Table 9-2.
SGN
The SGN function returns a +1 if its argument is positive, a -1 if
negative, and a if zero.
CONFIGURATION
SGN (a)
EXAMPLE
100 A = 100
200 X = SGN (A)
300 PRINT X
RUN
1
SIN
The SIN function returns the sine of the angle specified as its
argument. The argument will be assumed in radians unless a DEG
statement precedes the SIN statement.
176 User's Handbook to the Atari 400/800 Computers
CONFIGURATION
X = SIN (a)
EXAMPLE
10 DEG
20 X = SIN (90)
30 PRINT X
RUN
1
SOUND
The SOUND statement is used to output sound via the television
set or monitor's speaker.
The SOUND statement is used with the following configuration.
SOUND voice, pitch, distortion, volume
Together these four arguments determine the sound produced.
voice sets one of four voices available with the Atari. These are
numbered from to 3. These four voices are independent of
each other. In other words, as many as four voices can be
sounded at the same time.
pitch sets the pitch of the sound produced by the SOUND
statement. The pitch can range from to 255. The highest pitch
begins at and the lowest at 255.
The SOUND statement can produce either pure or distorted
tones, distortion can range between and 15. A distortion value
of 10 or 14 will produce a pure tone. Any of the other even
distortion values (0, 2, 4, 6, 8, 10, and 12) will generate a different
amount of noise into the tone produced. The amount of this
noise will depend upon the distortion and pitch values specified.
The odd numbered distortion values (1, 3, 5, 7, 9, 11, 13) cause
the voice indicated in the SOUND statement to be silenced. If
the voice is on, an odd-numbered distortion value will result in
its being shut off.
Atari BASIC Reference Guide 177
The volume controls the loudness of the voice indicated in
SOUND, volume ranges from (no sound) to 15 (highest
volume).
An Atari BASIC statement with a volume of will turn off the
sound. Sound can also be turned off by executing an END, RUN,
NEW, DOS, CSAVE, or CLOAD. If the System Reset key is
pressed, sound will be turned off. However, if the Break key is
pressed, sound will not be turned off.
SQR
SQR returns the square root of its argument.
CONFIGURATION
SQR (a)
EXAMPLE
10 X =49
20 PRINT SQR (X)
RUN
7
STATUS
STATUS returns a code which identifies the last input/output
operation undertaken on the channel specified.
CONFIGURATION
STATUS #channel, X
The status code will be returned via the numeric variable
indicated. The status codes are listed in Table 5-3.
EXAMPLE
100 STATUS #5, ST4
200 PRINT ST4
RUN
130
178 User's Handbook to the Atari 400/800 Computers
In the preceding example, the status code for the last
input/output activity undertaken on the device opened as
channel 5 is displayed.
Table 5-3. STATUS Code Values
STATUS Code
Reference
1
3
128-171
Operation completed with no problem.
Approaching end of file, Next READ
receives last data in file.
Reference Error Messages 128-171
in Appendix A.
STICK
The STICK function returns the position of the joystick indicated
as its argument.
CONFIGURATION
STICK (a)
"a" indicates the joystick number (0-3). The value returned can
range from to 15 and corresponds to the positions indicated in
Illustration 5-1.
EXAMPLE
IF STICK (1) = 7 THEN GOTO 700
Atari BASIC Reference Guide 179
Illustration 5-1. STICK Joystick Positions
STRIG
The STRIG function returns a value of if the specified joystick's
button is depressed. A 1 is returned if the button is released.
CONFIGURATION
STRIG (a)
"a" indicates the joystick number (0-3).
EXAMPLE
100 IF STRIG (2) = THEN GOTO 700
180 User's Handbook to the Atari 400/800 Computers
STOP
The STOP statement causes a halt in the execution of a BASIC
program.
CONFIGURATION
STOP
When a STOP statement is executed, the computer will return to
graphics mode 0. If STOP is executed in the program mode, the
following screen message will be displayed;
STOPPED AT LINE XXX
where XXX is line number where STOP was executed. If STOP is
executed in the immediate mode, this message will not appear.
CONT can be used to rescue program execution after it was
halted by executing STOP.
EXAMPLE
100 INPUT A
105 IFSGN (A) =-1 THEN 150
110 B = SQR (A)
120 IF SGN (B)<>1 THEN STOP
130 PRINT B
140 GOTO 100
150 END
In the preceding example, if a value of is input for A in line 100,
program execution will stop and the following message will be
displayed.
STOPPED AT LINE 120
By entering CONT, program execution will resume with line 130.
Atari BASIC Reference Guide 181
STR$
STR$ returns the string representation of its argument.
CONFIGURAITON
a$ = STR$(a)
In the following example, A$ would consist of the string "40". In
this case, "40" is a string— not a number. In other words, "40" (in
its string equivalent) would not be used in calculations.
EXAMPLE
050 DIM A$(50)
150 A$ = STR$(40)
200 PRINT A$
RUN
40
TRAP
The TRAP statement causes program execution to branch to the
line number indicated when an error is encountered.
CONFIGURATION
TRAP LN
TRAP must have been executed prior to the occurrence of the
error. Otherwise, a branch to the indicated program line will not
take place.
TRAP will invalidate the Atari's automatic error handling routine
which halts program execution.
182 User's Handbook to the Atari 400/800 Computers
EXAMPLE
100 TRAP 700
200 INPUT A
300 IF A = THEN 999
400 PRINT A
500 GOTO 200
700 PRINT PEEK (195)
800 PRINT 256 * PEEK (187) + PEEK (186)
999 END
RUN
?A
8
200
READY
In the preceding example, the TRAP statement in line 100 will
cause the program to branch to line 700 if an error is
encountered. In line 700, the error code is displayed. (Address
195 is used to store the error code.). In line 800, the line number
where the error occurred isdisplayed.Thefollowingexpression,
256 * PEEK(187) + PEEK(186)
returns the line number where the error occurred.
In our example, the data input in response to the INPUT
statement in line 200 was string. Since a numeric variable was
specified in line 200, error code 8 was generated. This was
displayed along with the line number where the error occurred
(200).
USR
USR is used to branch program control to a machine language
program.
CONFIGURATION
USR(address[, argument ...])
Atari BASIC Reference Guide 183
The address indicated is that of the machine language
subroutine to be branched to. Function arguments between
and 65535 can be optionally included with the USR command as
indicated in the Configuration.
Beginning with the last argument, each argument is evaluated
and converted to a 2-byte hexadecimal integer. This integer is
placed on the hardware stack, and a count of the USR arguments
is also pushed on the stack. The hardware stack configuration is
depicted in Illustration 5-2.
Returning To BASIC
When BASIC executes a USR function, the BASIC program's
current location is pushed onto the hardware stack (see
Illustration 5-2). The machine language program can return to
BASIC by executing the assembly language RTS instruction. RTS
will pull the return location within the BASIC program from the
hardware stack.
However, before RTS can be used to pull the return location off
the stack, all data on the stack related to function arguments
must have been pulled off the stack. This includes both the
arguments themselves as well as the argument count. Even if
there are not arguments, the machine language program must
pull the argument count off the stack before returning to the
BASIC program.
VAL
The VAL function converts its string argument to a numeric
value. The first character of the string argument must be a
numeric character. Otherwise, an error will occur. The numeric
characters in the string argument will be converted to their
numeric equivalents until a non-numeric string character is
encountered.
CONFIGURATION
VAL (a$)
184 User's Handbook to the Atari 400/800 Computers
Illustration 5-2. USR Hardware Stack
Top of Stack
Bottom of Stack
USR Argument Count
First USR Argument
Second USR Argument
Final USR Argument
BASIC Program's
Return Address
Stack Contents Prior
to USR
XIO
EXAMPLE
050 DIM A$(50)
100 A$ = "57A72B"
200 PRINT VAL(A$)
300 PRINT VAL(A$) + 2
RUN
57
59
The XIO statement is a generalized input/output statement
which can perform a wide range of input and output operations.
These operations are summarized in Table 5-4.
Atari BASIC Reference Guide 185
CONFIGURATION
XIO command, #channel, a, b, device
The command value (as specified in Table 5-4) indicates the
operation to be performed. The channel specified must have
been previously opened for input or output (with the exception
of XIO 3).
The numeric expressions (a, b) are not always used by XIO,
however, they must always be present as parameters. The
applicable numeric expression values are given in Tables 5-4, 5-5,
5-6, and 5-7.
The final parameter, device, specifies the device to be used for
the input/output operation.
Table 5-4. XIO Command Summary
DOS or BASIC
Operation
Command
Counterpart
Numeric Exp1
Numeric Exp2
General I/O Operations:
Open a channel
3
OPEN
See Table 5-1
0-8
Read a line
5
INPUT
Get a character
7
GET
Write a line
9
PRINT
Put a character
11
PUT
Close channel
12
CLOSE
Status of channel
STATUS
Screen Graphics:
Draw a line
17
DRAWTO
Fill an area
18
None
Disk*:
Rename a file
32
DOS Menu E
Delete a file
33
DOS Menu D
Lock a file
35
DOS Menu F
Unlock a file
36
DOS Menu G
Move file pointer
37
POINT
Find file pointer
38
NOTE
Format diskette
254
DOS Menu 1
°
•DOS must have been booted.
186 User's Handbook to the Atari 400/800 Computers
RS-232 Serial Port:
Output Port of a Block
32
None
Control DTR, RTS, XMI
34
None
See Table 5-5
Baud rate, word size,
36
None
See Table 5-6
See Table 5-6
stop bits, & ready
monitoring
Translation mode
38
None
See Table 5-7
ASCII Code
Concurrent mode
40
None
Table 5-5. Numeric Expression 1 Values for XIO 34
Function*
DTR
RTS
XMT
No change
Turn Off (XMT to 0)
Turn On (XMT to 1)
128
192
32
48
2
3
*Add value for DTR, RTS, & XMT to obtain Numeric Expression 1
Example Values
DTR
RTS
XMT
of Numeric Expression 1
162
Off
Off
163
Off
Off
1
178
Off
On
179
Off
On
1
226
On
Off
227
On
Off
1
242
On
On
243
On
On
1
Atari BASIC Reference Guide 187
Table 5-6. Numeric Expression 1 and 2 Values
For XIO 36
Numeric Expression 1 Value*
Stop Bits
Value
Word Size
Value
Baud Rate
Value
1
8 bits
300
2
128
7 bits
16
45.5
1
6 bits
32
50
2
5 bits
48
56.875
75
110
134.5
150
300
600
1200
1800
2400
4800
9600
9600
3
4
5
6
7
8
9
10
11
12
13
14
15
*Add value from each column to determine Numeric Expression
Numeric Exp
ression
2 Value
DSR
CTS
CRX
Value
No
No
No
No
No
Yes
1
No
Yes
No
2
No
Yes
Yes
3
Yes
No
No
4
Yes
No
Yes
5
Yes
Yes
No
6
Yes
Yes
Yes
7
188 User's Handbook to the Atari 400/800 Computers
Table 5-7. Numeric Expression 1 Value for XIO 38
Numeric Expression 1*
Line Feed
Translate Atari
ASCII to ASCII
Input Parity
Output Parity
Append
Value
Mode
Value
Mode
Value
Mode
Value
No
Yes**
64
Light
Heavy
None
16
32
Disregard
Odd
Even
Disregard
4
8
12
No change
Odd
Even
Bit On
1
2
3
*Add one value from each column to determine Numeric Expression 1.
"The line feed character is appended after a carriage return (EOL).
EXAMPLE
XIO Example Program
100 GRAPHICS 5
200 COLOR 1
300 PLOT 50,20
400 DRAWTO 50,10
500 DRAWTO 10,10
600 POSITION 20,20
700 POKE 765,1
800 XIO 18,#6,0,0,"S:"
The preceding example illustrates the use of the XIO command
to fill an area in graphics. The command, 18, specifies the
graphics fill area action. Channel #6 is the graphics channel. The
numeric parameters are both specified as 0, and the device is the
screen (5:).
CHAPTER 6.
ATARI 410 PROGRAM RECORDER
Introduction
The Atari 410 Program Recorder is used for storing BASIC
programs or data on cassette tape. BASIC programs or data can
be transferred from RAM onto cassette via any one of several
Atari BASIC statements.
The process of transferring a program from RAM onto cassette
tape (or any other storage device) is known as saving that
program. Once a program has been saved, it can later be
transferred back from the storage device into RAM. This process
is known as loading.
Data can also be transferred back and forth between RAM and
cassette tape. The process of sending data to cassette tape is
known as writing the data. The retrieval of that data from cassette
tape back into RAM is known as reading the data.
In this chapter, we will discuss the BASIC statements used to read
and write data and to save and load programs. However, first we
will discuss the concepts of data and program storage.
Data Files-Files, Records, & Fields
Data files can be visualized as being organized as files, records,
or fields.
If we visualized the Atari 410 Program Recorder as a filing
cabinet, a data file would be analogous to one file within that
filing cabinet. For instance, if you kept a file filled with slips of
paper containing the names and addresses of all of your cousins,
that physical file would be analogous to a computer's data file.
190 User's Handbook to the Atari 400/800 Computers
Your data file could contain any number of slips of paper-
depending upon how many cousins you had. Each slip of paper
containing the name and address of one of your cousins would
be analogous to a record with a data file.
Each individual data item within a record is known as a field. In
our example, the name of each cousin might be considered a
field as well as the street address, city, state, zip code, and
telephone number.
Program Files
Programs are also stored as files. However, unlike data files,
program files are not divided into records and fields.
We will discuss loading and saving program files in the following
several sections. The reading and writing of information to data
files will be discussed later in this chapter.
Saving Programs on the Atari 410
Atari BASIC contains three statements that are used to store
programs on cassette tape. These are:
CSAVE
SAVE
LIST
Each of these three statements has a corresponding Atari BASIC
statement which is used to load a program into memory from the
cassette tape. These are:
CLOAD
LOAD
ENTER
The CSAVE statement is used only for saving programs on
cassette. LIST and SAVE can be used to send a program to devices
other than the Atari 410 Program Recorder. LIST and SAVE must
Atari 410 Program Recorder 191
be used with the Program Recorder's device name (C:) as shown
below,
LIST "C:"
SAVE "C:"
to save programs on the Program Recorder.
Either the CSAVE or SAVE "C:" statements will save the complete
program when executed. The LIST"C:" statementcan be used to
save either all or part of a program. The following LIST statement
would save line numbers between 500 and 1000 to the 410
Program Recorder when executed.
LIST "C" 500, 1000
When either the CSAVE, LIST "C:", or SAVE "C:" statements are
executed, the Atari's speaker will sound twice. This is a signal for
the operator to place a cassette tape in the 410 Program
Recorder. The tape should then be forwarded to the position
when recording is to begin. The rewind and fast forward keys can
be used to position the tape.
Once the tape is in the proper position, press the record and play
keys. When the tape is ready, press Return on the Atari keyboard
and the recording process will begin.
By turning up the sound on your television set or monitor, you
can actually hear the recording process. A high pitched tone will
be sounded followed by a number of short eruptions of sound.
Each sound indicates that a block of program information has
been saved on the cassette. When the program has been
recorded, the sounds will stop and the tape will stop. The user
should then press the stop key on the Atari 410 Program
Recorder.
Program Recording Formats
Each of the three Atari BASIC statements used to record
programs do so using a different format. These different formats
are not discernable to the user. However, the user must keep in
192 User's Handbook to the Atari 400/800 Computers
mind the format used to save an Atari program if he wishes to
successfully load that program.
The CSAVE and SAVE statements record programs in tokenized
format. In this format, Atari BASIC keywords are abbreviated
with one character tokens. The computer automatically encodes
the keywords as tokens.
Although both the SAVE and CSAVE statements record programs
in tokenized format, differences remain in the exact format
used. Programs are recorded in groups of data known as blocks.
The difference between SAVE and CSAVE lies in the amount of
space allowed to remain between the blocks of data.
The CSAVE statement allows less space between these blocks of
data than does the SAVE statement. Therefore, saving or loading
a program with CSAVE and CLOAD will be accomplished in less
time than with SAVE "C:" and LOAD "C:".
CLOAD will load programs saved with either the CSAVE or SAVE
statements, while the LOAD statement will only load those
programs recorded with a SAVE statement.
The LIST statement saves programs in Atari ASCII format. An
ASCII code is saved for every character in the Atari BASIC
program. Keywords are not abbreviated as tokens. The ENTER
statement must be used to load programs saved with the LIST
statement.
Loading a Program on the Atari 410
As previously mentioned, the CLOAD statement is used to load
programs from cassette tape into RAM that had been
previously saved with the SAVE or CSAVE statements. Likewise,
the LOAD statement is used to load those programs previously
saved with the SAVE statement, and the ENTER statement is used
to load programs saved with the LIST statement.
The reason why certain statements must be used to load files
saved with corresponding statements lies in the format in which
the program was recorded. The LIST statement saves a BASIC
program file in Atari ASCII format, while SAVE and CSAVE
Atari 410 Program Recorder 193
transfer BASIC programs in tokenized format.
The ENTER statement can only load a BASIC file stored in ASCII
format. ENTER will not load BASIC files stored in tokenized
format.
LOAD and CLOAD can only load BASIC files stored in tokenized
format. CLOAD will load files saved with either SAVE or CSAVE,
but neither will load files saved with LIST.
LOAD can only load files saved with the SAVE statement in
tokenized format. LOAD cannot be used to load files saved with
CSAVE even though CSAVE stores BASIC files in tokenized
format, because CSAVE uses a timing pattern which is
uncompatible with LOAD. LOAD cannot be used with BASIC
programs saved with the LIST statement as these were saved in
ASCII format.
Both ENTER and LOAD can be used to transfer a program from a
device other than the Atari 410 program recorder. The CLOAD
statement can only be used to load a program from the Atari 410
into RAM.
When either LOAD or CLOAD are used to load a program, a
NEW statement will be automatically executed before the
program is loaded. This causes any existing programs or variables
to be erased from memory.
If the ENTER statement is used to load a program from the Atari
410, any existing program lines will not be erased from memory.
ENTER adds the program lines from the cassette file to any
existing program lines in memory. If a program line in the
program being transferred from cassette has the same line
number as a program line in memory, the program line being
transferred from cassette will replace the program line in
memory.
Also, when ENTER is used to load a program, any variables in the
variable name table (VNT) will not be erased. Any new variable
names encountered in the program being loaded will be added
to the existing variable names in the VNT.
194 User's Handbook to the Atari 400/800 Computers
The variable name table is a table kept by Atari BASIC of all
variable and array names used in a program regardless of
whether the program was entered in the immediate or the
program mode.
When the CSAVE or SAVE statements are used to save a BASIC
program, the variable name table is recorded with the program
lines. When CLOAD and LOAD are executed to load the
program lines back into RAM, the variable name table will also
be loaded and will replace any existing variable name table in
RAM.
Conversely, when the LIST statement isexecuted tosavea BASIC
program, the variable name table will not be saved. Therefore,
when the ENTER statement is executed to load the program
saved by LIST back into memory, no variable name table will be
loaded and the variable name table currently held in RAM will
remain. When the BASIC program loaded with ENTER is
executed, any variableand array names used in that program will
be added to the variable name table.
If programs are continually saved and loaded with LIST and
ENTER statements, the variable name table may eventually
become overcrowded with unused variable and array names. It
may become necessary to clear the variable name table.
This can be accomplished by first saving the existing program in
RAM using the LIST statement. Next, by executing the NEW
statement, the variable name table (as well as the existing
program in RAM) will be erased. The program can then be
loaded back into RAM using the ENTER statement. As the
program is executed, variable and array names will be added to
the variable name table.
When either of the following statements,
CLOAD
ENTER "C:"
LOAD "C:"
are executed, the following series of events will occur.
Atari 410 Program Recorder 195
1. The computer's built-in speaker will sound onetime. This is
a signal to the operator to place the cassette containing the
program to be loaded in the Atari 410 Program Recorder.
2. Use the rewind and fast forward keys to position the tape to
the area on the tape near the beginning of the program. It is
a good practice to save a program at the beginning point of
a tape as it is then easy to locate.
For programs not recorded at the beginning of a tape, the
410's tape counter can be used to locate a program's
beginning position.
3. Once the beginning position of the program on the tape is
located, the play button on the 410 Program Recorder
should be pressed. Also, the Return key on the Atari
computer's keyboard must be pressed to signal the
computer that the cassette is ready.
4. The cassette tape will then begin moving as the program is
loaded into memory. By turning up the volume on your
monitor or television set, you can actually hear the
program being loaded. You will hear short eruptions of
sound followed by long periods of silence. Each sound
eruption is emitted as a block of data is loaded from the
cassette.
When the sound eruptions stop, the tape will stop as well.
The entire program has now been loaded into RAM. The
stop key on the 410 Program Recorder should then be
pressed to stop the tape.
RUN "C:" Statement
The RUN "C:" statement is a variation of the RUN statement
which allows the user to both load and run a program from the
410 Program Recorder in a single step.
The RUN "C:" statement is in fact a combination of the LOAD
"C:" and RUN statements. Therefore, RUN "C:" can only be used
to load programs saved with the SAVE "C:" statement.
196 User's Handbook to the Atari 400/800 Computers
The RUN "C:" statement can be used in the program mode as
well as the immediate mode to load and execute a program. For
example, suppose the following program was input and saved on
cassette:
NEW
READY
100 PRINT "ONE. TWO. THREE"
200 PRINT "PRESS RETURN TO LOAD"
300 RUN "C:"
SAVE "C:"
READY
A second program could then be input and saved as shown in the
following example:
NEW
READY
100 PRINT "FOUR, FIVE, SIX"
SAVE "C:"
READY
The cassette tape now contains two consecutive programs. By
rewinding the tape, entering "NEW", and executing the RUN
"C:" statement, the first program will be loaded and executed.
When line 300 is executed, the RUN "C:" statement will cause
Atari 410 Program Recorder 197
the Atari's speaker to beep. When the operator presses the
Return key on the Atari's keyboard, the second program will be
automatically loaded and executed.
Notice the inclusion of the prompt statement in line 200 of the
first program to remind the operator to press the Return key. The
output from the loading and execution of our examples should
appear as in the following:
RUN "C:"
ONE, TWO, THREE
PRESS RETURN TO LOAD
FOUR, FIVE, SIX
READY
This procedure of loading the program from another is known as
chaining. When chaining programs using the RUN statement,
remember that a NEW statement is automatically executed
causing the existing program in memory as well as the variable
name table to be erased. This prevents a program from using the
same variable values that were used in a previous program from
which it was chained.
Reading and Writing Data
Atari BASIC uses the PRINT* and PUT statements to write data to
the 410 Program Recorder. The INPUT* and GET statements are
used to read data stored on cassette back into RAM.
When data is being transferred between RAM and the 410
Program Recorder, it is transferred in blocks of 128 characters. A
portion of memory is reserved to hold one 128 character block of
data that is to be read from or written to the 410 Program
198 User's Handbook to the Atari 400/800 Computers
Recorder. This area of memory is known as the cassette buffer.
As mentioned earlier in this chapter, data is organized into files,
records, and fields. The notion of files, records, and fields relate
to a programmer's conception of how a data file is organized.
In actuality, a cassette data file physically consists of three
separate parts: the leader, data blocks, and an end-of-file
record.
The 20 second data file leader allows the Atari computer and 410
Program Recorder to synchronize their timing so that data may
be transferred. The actual data is stored in blocks of 128
characters each.
The last block (known as the end-of-file block) can consist of
fewer than 128 characters of data. This block holds the final
characters of the data file (i.e. Those characters still remaining
after the last complete block has been utilized.).
Records can consist of more than one block, less than one block,
or exactly one block. The computer will assign records to data
blocks automatically. The programmer need not concern
himself with this process.
Opening Data Files
Before information can be read from or written to a data file, that
file must first be opened. This is accomplished with the OPEN
statement.
The data file can be read from or written to as long as it is open.
To prevent access to the file, it must be closed. This is
accomplished with the CLOSE statement.
The OPEN statement uses the following configuration:
OPEN ^channel, task, value, device
OPEN can be used with external devices other than the 410
Program Recorder including the disk, screen, keyboard, printer,
Atari 410 Program Recorder 199
and RS-232 port.
The following is an example of an OPEN statement used to open
a data file for access by the 410 Program Recorder.
OPEN #1,4, 0, "C:"
The first parameter in the OPEN statement indicates the
channel. Before an external device can be accessed either for
input or output, a channel to the device must have been opened.
The OPEN statement assigns a channel to an external device.
Once a channel is assigned, the device can subsequently be
accessed via its channel number. Only one channel can be open
at any one time. If an OPEN channel attempts to open a channel
which is already open, an error will occur.
The second parameter in the OPEN statement indicates the
activity for which the channel is being opened. For the 410
Program Recorder, a value of 4 indicates the channel is being
opened to read data while a value of 8 indicates the channel is
being opened to write data. A cassette file cannot be
simultaneously open for both input and output.
The third parameter in the OPEN statement isOfor standard data
files. The final parameter, device, must be specified as "C:" for
input or output to the 410 Program Recorder.
When a cassette data file is opened for input or output, the
Atari's speaker will be sounded once for input or twice for
output to signal the operator to properly position the tape. Once
the tape has been properly positioned, the usershould press the
410's play button, and then press any key on the Atari.
If the file was opened for output, the computer will write the
leader. If the file as opened for output, it will read the leader.
This process requires approximately 20 seconds.
Once the leader has been read or written, the program must
read or write data to the open file. If the file was opened for
output, data must be written to the file. If the program fails to
200 User's Handbook to the Atari 400/800 Computers
immediately write data to a newly opened file, an error may
result if an attempt is later made to read the file.
If the file was opened for input, the program must read data from
the file with a GET or INPUTS statement. If the program fails to
read data from the open file, an error may occur if the program
subsequently attempts to read data in the program.
Closing Data Files
Once an open file has been accessed, it is important to close that
file so that the file's channel can be assigned elsewhere.
Also, if the channel is open for output, closing it causes any
remaining data in the cassette buffer to be output followed by an
end-of-file record. If the open file is not closed, any remaining
data in the cassette buffer may be lost.
The following CLOSE statement,
CLOSE #4
will close channel 4.
All open files are closed automatically when an END or RUN
statement is executed, or when a program's last statement is
executed (only in the program mode).
Writing to a Data File
As mentioned previously, the PRINTS and PUT statements can be
used to send data from RAM to the cassette data file. Both
PRINTS and PUT specify an open channel as their first parameter.
The data being output will be sent via the channel indicated.
That channel must be open.
The PRINTS statement uses the following configuration when
used to output data to a cassette file.
PRINT Uchannel; expression...
Atari 410 Program Recorder 201
channel indicates the channel to be used to send the output.
Semicolons should be used rather than commas to separate the
channel from the first expression, as well as to separate any
subsequent optional expressions. The use of commas is allowed,
but this practice would cause additional blank spaces to be
inserted in the file. Each separate expression should end with an
EOL character. This can be accomplished by using one PRINT*
statement for each expression or by using CHR$(155).
The expressions consist of one or more string or numeric values
to be output. These values are output as ASCII values.
Always be sure that a PRINT# statement being used to output
data to a cassette file outputs an end-of-line (EOL) character
after each expression. The PRINT# statement sends data to the
cassette buffer where it is stored until it is filled. The entire block
of data (128 bytes) is then sent to the Atari 410.
If an EOL character is output at the end of the PRINT# statement,
the data in the cassette buffer will be output to the cassette file,
regardless of whether the buffer is full or not. In these situations,
the 128th character in the buffer will contain the actual number
of bytes in the buffer. This value is stored in the hex form.
PRINT* statements automatically output an EOL character after
outputting the expressions unless a comma or semicolon is
placed at the end of the expression list. For this reason, never
end a PRINT* statement with a comma or semicolon, when it is
being used to output data to a cassette file. An example of the
use of PRINT* is given below.
400 OPEN #2, 8, 0, "C:"
500 PRINT#2; "JOHN"
550 PRINT#2; "JACK"
600 CLOSE #2
The PUT statement can be used to output a single numeric value
to the cassette file via an open channel. PUT uses the following
configuration:
PUT #channel, numeric expression
202 User's Handbook to the Atari 400/800 Computers
As with PRINT*, the channel specified must be open for output.
The value given in numeric expression is output to the data file.
The value output will lie between Oand 255. If the value is not an
integer, it will be rounded to the nearest integer.
If the value specified does not lie between and 255, it will be
output modulo 256. In other words, 256 would be sent as 0,257 as
1, 258 as 2, 259 as 3, etc.
An example of a PUT statement is given below.
150 OPEN #2, 8, 0, "C:"
160 PUT #2, 123
170 CLOSE #2
Reading from Data Files
The INPUT* and GET statements are used to read data from
cassette data files. INPUT# will accept data from the cassette data
file, interpret that data, and assign the data to the variable or
variables names in its parameter list.
The following configuration is used with INPUTS:
INPUT #channel J ! I variable,...
The channel must have been opened previously for input. The
variables will accept the data values input.
INPUTS will retrieve data from the input device specified. This
data will consist of ASCII characters followed by the ASCII end-
of-line character. The EOL character will end input to the
variable specified.
INPUTS will interpret the data being read as either numeric or
string— depending on the type of variables used as parameters.
When a numeric variable is specified, the data being input will
be interpreted as numeric data.
The data read via INPUTS will be assigned to the numeric
variable indicated until a comma or an EOL character is
Atari 410 Program Recorder 203
encountered. Numeric values can be ended either with the EOL
character or the comma. Commas can not be used to end string
values, as they are regarded as part of the string.
If no data is available to be read into the numeric variable, or if
the data is invalid, an error will result.
When a string variable is specified, the data being input will be
interpreted as string data. If no characters are read, the string
variable will be assigned the null value. If more characters are
read than allowed for in the string variable's DIM statement, the
INPUT# statement will disregard the excess characters. The EOL
character will end the string input.
The GET statement is used to read a single numeric value via the
open channel specified. GET uses the following configuration.
GET Uchannel, numeric variable
The cbannel specified must be open for input. The numeric
variable indicated will accept the value returned by GET. This
value will lie between and 255.
When GET is used with the 410 Program Recorderand the buffer
is empty, the initial GET statement will result in a block of data
being read into the cassette buffer. The first value in the buffer
will be assigned to the numeric variable specified with the first
GET statement.
Each successive GET statement will read a value from the cassette
buffer. When the buffer has been emptied, another block of
data will be read into the cassette buffer from the cassette tape.
CHAPTER 7.
ATARI 810 DISK DRIVE
Introduction
The Atari 810 Disk Drive is used for storing BASIC programs or
data files on floppy diskettes.
A disk stores data in a magnetic form, much like data is stored on
magnetic tape. The main difference between storage on a
magnetic tape and storage on a disk is that the disk surface is
round— much like a record's surface.
The disk drive contains a device known as a read/write head,
which is used to read and write information. The computer can
move the head to any position desired on the disk surface. This is
in contrast to magnetic tape, where data is read from or written
onto the tape in consecutive order.
This capacity to read or write data at a particular position is
known as random access. Disk drives are known as random
access storage devices. On the other hand, in cases where data
must be read or written in a consecutive order, the accessing is
known as sequential access. A cassette tape recorder is known as
a sequential access drive.
Types of Disks
There are three primary types of disks used by microcomputers;
hard disk, Winchester disks, and floppy diskettes. These will be
described in the following sections.
Hard Disks
Microcomputer hard disk systems generally allow storage of 5 to
30 megabytes of data. One megabyte is the equivalent of one
206 User's Handbook to the Atari 400/800 Computers
million bytes. The hard disk itself is made of a rigid material with
a magnetic coating. The disk drive and the hard disk are separate
units. The operator can remove one hard disk and replace it with
another.
Winchester Disk Drives
Winchester disk drives are designed so that from 6 to 10 times
more data can be stored on their surface than on a standard
floppy diskette. Winchester disks must be kept very clean as they
are extremely vulnerable to dust, dirt, and smoke.
Since they must be kept so clean, Winchester disks must be
sealed inside of the disk drive. This means that Winchester disks
cannot be changed.
Since Winchester disks cannot be removed, floppy disk systems
often are used in conjunction with Winchester disks to allow for
back-up storage. Winchester disk systems are generally used
with microcomputers rather than hard disk systems. A
Winchester drive is shown in Illustration 7-1.
Illustration 7-1. Winchester Disk System
Atari 810 Disk Drive 207
Floppy Diskettes
The most widely used type of disk storage with microcomputers
is floppy disk storage. A floppy diskette consists of a round vinyl
disk which is enclosed within a plastic cover. The diskette is
generally stored in a diskette envelope.
This cover protects the diskette from damage while it is being
handled by the operator. The diskette should never be removed
from its cover. A 5V4 inch diskette with its protective envelope is
shown in Illustration 7-2.
The diskette is allowed to rotate within the protective envelope.
The round hole in the middle of the diskette a I lows the disk drive
to hold the diskette and spin it. The oblong shaped opening on
the protective envelope provides an area where the head can
read from or write to the diskette surface.
Illustration 7-2. Mini-Floppy Diskette
Temporary Label
Permanent
Label
Diskette in
Protective Cover
Exposed Read/Write
Head Slot
Diskette
Envelope
Write Protect Notch
(Some diskettes do
not have this notch)
Index Hole
208 User's Handbook to the Atari 400/800 Computers
Floppy diskettes come in two sizes: 8 inch and 514 inch. The 514
inch diskettes are also known as mini-floppy diskettes. The Atari
810 Disk Drive uses mini-floppy diskettes.
Tracks & Sectors
To facilitate the process of searching for data on the diskette
surface, that surface is divided into tracks and sectors.
Tracks may be visualized as a series of concentric circles on the
diskette surface, as shown in Illustration 7-3. Atari's DOS divides
a diskette into 40 tracks.
To further reduce the time necessary to search for a particular
data item, Atari's DOS divides each track into 18 sectors, which
are also shown in Illustration 7-3.
With 40 tracks available and 18 sectors per track, Atari DOS
divides each diskette into 720 sectors. However, 18 of these 720
sectors are used by Atari DOS, and cannot be used to store
programs or data.
Illustration 7-3. Tracks and Sectors
^---^.
// /
-Track
Atari 810 Disk Drive 209
Each individual sector holds 128 bytes of data. When DOS has
access to the track and sector where a particular data item is
being stored, it will only have to search 128 bytes to find that
item. The result of dividing the diskette surface into tracks and
sectors is that access time is greatly decreased.
Hard and Soft Sectors
Locating a particular track on the disk surface is a relatively
uncomplicated matter. The drive merely moves the head to the
position on the diskette where the specified track is located,
much like the needle on a phonograph is positioned to the
location of a specific song on a record album.
However, locating a particular sector is a more difficult process.
Two different methods are used to locate sectors on a disk; hard
sectoring and soft sectoring.
Both the hard and soft sector methods involve the use of an
index hole. The index hole is shown in Illustration 7-2. It is
located just to the right of the large hole in the middle of the SVa
inch diskette.
The index hole, as shown in Illustration 7-2, is a hole only in the
diskette's protective covering. Another index hole is located on
the actual diskette surface inside the envelope. As the diskette
spins, the index hole (or holes) on the diskette surface passes
underneath the hole in the protective envelope.
A light source inside the disk drive shines light onto the area of
the diskette containing the index hole. When an index hole on
the disk surface is aligned with the index hole on the protective
envelope, the light will shine thro ugh to a sensor. The sensor will
relay information on the location of the index holes, which can
be used to calculate the various sector locations.
Now that we have discussed the concepts of locating sectors, we
will discuss the difference between hard and soft sectored
diskettes. A hard sectored diskette contains a number of holes,
each of which indicates the location of a sector. An extra hole is
used to indicate the location of the first sector. The location of
210 User's Handbook to the Atari 400/800 Computers
the various sectors is determined by counting the number of
holes occuring after the first sector. A hard sectored diskette is
depicted in Illustration 7-4.
Soft sectored diskettes have only one index hole as shown in
Illustration 7-5. This solitary index hole marks the location of the
first sector. By timing the rotation speed of the floppy diskette,
the location of the other sectors can be determined. The Atari
810 uses soft -sectored diskettes.
Illustration 7-4. Hard Sectored Diskette
2 Index
Holes
Sector
Atari 810 Disk Drive 211
Illustration 7-5. Soft Sectored Diskette
Index Hole
Sector
Single and Double Sided Diskettes
Some floppy diskettes are designed to be written on only one
side. These are known as single sided (SS) diskettes.
Diskettes which are designed to be written on both sides are
known as double sided (DS) diskettes.
Single, Double and Quad Density Diskettes
Density refers to a diskette's recording format, which in turn
affects its capacity. Single density 514 inch diskettes have roughly
94K of capacity, double density 514 inch diskettes have a capacity
of about 140-160K, and quad density 514 inch diskettes have a
capacity of up to 370K.
The Atari 810 uses single sided single density diskettes. The Atari
810 has a total storage capacity of 88,375 bytes. This figure is
calculated by multiplying the 707 sectors available for data
storage by 125 bytes per sector. Three bytes per sector are
allocated for the File Management Subsystem.
212 User's Handbook to the Atari 400/800 Computers
Diskette Write Protection
Diskettes have a notch on the side of their protective envelope
which determines whether or not data can be written onto that
diskette. On 8 inch diskettes, this notch is known as a write-
protect notch. On 514 inch diskettes, it is known as a write-
enable notch.
On an 8 inch diskette, information cannot be written onto the
diskette unless this notch has been covered. On 514 inch
diskettes, information cannot be written onto the diskette unless
the notch is left uncovered.
Some 514 inch diskettes (especially system diskettes) may be
permanently write protected if their protective envelope does
not contain a notch. Any 5 1 /4 inch diskette with a notch can be
write protected by merely covering the notch with a piece of
tape as shown in Illustration 7-6.
Illustration 7-6. Write Protecting a 514 Inch Diskette
Atari 810 Disk Drive 213
Disk Files
The Atari 810 stores data in files. A disk file can contain either a
BASIC program, a machine language program, or data. An Atari
diskette can contain as many as 64 files.
Files are assigned unique filenames of up to eight characters. The
first character of a filename must be a capital letter. Subsequent
filename characters can either be capital letters or numbers.
Blank spaces, punctuation marks, and special characters (#,$, @)
are not allowed in filenames.
Filenames can also contain a filename extension of three or
fewer characters. The filename and filename extension must be
separated with a period. Filename extensions can contain either
letters or numbers.
Filename extensions are often used to indicate the type of file.
The implied meanings of commonly used filename extensions
are listed in Table 7-1.
Filename Match Characters
Atari DOS allows the use of the filename match characters , ?and
*. These characters can be used to stand for any single character
(?) or group of characters (*). For example, FILE?. DAT would
match the following filenames.
FILE1.DAT
FILEZ.DAT
FILE?. DAT would not match the following filenames:
FILE. DAT
FILE1.BAS
FILE.* would match any of the following filenames.
FILE.BAS
FILE.TXT
FILE. DAT
214 User's Handbook to the Atari 400/800 Computers
Filename match characters are not allowed in Atari DOS version
1.0, and can only be used with the following DOS menu options
in DOS version 2.0.
A. Disk Directory
B. Copy File
D. Delete File
E. Rename File
F. Lock File
G. Unlock File
O. Duplicate File
Table 7-1. Filename Extensions & Type of File
Filename
Extension
File Type
ASM
Assembly language source file.
BAK
Backup File.
BAS
File containing a Basic program
in tokenized format.
DAT
Data File.
OBJ
Assembly language program
assembled into machine language.
Also known as an object file.
TXT
Text File.
SYS
System file. Used with system pro-
grams such as DOS programs or the
BASIC language interpreter.
Atari 810 Disk Drive 215
ATARI DOS (Disk Operating System)
An operating system can be defined as a group of programs
which manage the computer's operation. A disk operating
system can be defined as a group of programs that manage the
transfer of data to and from a storage device such as disk or
magnetic tape.
Two different versions of Atari DOS currently exist, DOS 1.0 and
DOS 2.0. The version your system uses should be marked on your
system diskette.
The major differences between DOS 1.0 and 2.0 are listed in
Table 7-2.
Table 7-2. DOS Version 1.0 & 2.0 Differences
DOS 1.0
DOS 2.0
11 second boot time
No filename match char-
acters
MEM.SAV not available
No AUTORUN.SYS
No appending of files
Bad diskette sectors
not indicated during
formatting
7 second boot time
Filename match characters
allowed during certain DOS
operations
MEM.SAV allows additional
memory space
AUTORUN.SYS allows a file
to be loaded and executed
upon boot
SAVE BINARY FILE "/A"
option allows appending of
two files
A diskette with bad sectors
cannot be formatted
216 User's Handbook to the Atari 400/800 Computers
Menu must be displayed
Menu need not be re-
before a new command
displayed to enter a
can be entered
new command
DOS files can only be
DOS files can be written
written to Drive 1
to any drive
NOTE/POINT not avail-
NOTE/POINT statements
able for random access
available for random access
A maximum of 3 files
Up to 8 files can be
can be open at any
open at any one time
one time
Two Parts of Atari DOS
Atari DOS consists of two different parts. One part is used to save
and load BASIC programs and to read and write data files. The
other part of Atari DOS consists of a group of utility programs
used in performing operations with disk files as well as reading
and writing machine language files.
In DOS version 1.0, both parts of DOS are stored as a single file
on disk. This file is named DOS. SYS.
In DOS version 2.0, the two parts of DOS are stored on disk as
two separate program files. The first part (DOS. SYS) is needed
whenever the disk drive is being used. The second part
(DUP.SYS) is only required when the disk utilities are being used.
By separating DOS in version 2.0, better use can be made of the
Atari's memory. Only the part of DOS required need be loaded
into memory. The portion of memory normally used by the
other part of DOS is freed for use.
Atari 810 Disk Drive 217
Disk Buffer
Atari DOS controls the transfer of information between the Atari
computer and the disk drive. Information is transferred in 128
character blocks.
Four separate portions of Atari RAM are set aside to hold data
being transferred to a disk from a disk drive. These are known as
disk buffers. The reason why there are four disk buffers is that as
many as four disk drives can be attached to the Atari at any one
time.
When Atari DOS is instructed to supply data, it will first attempt
to supply this data from the disk buffer. When the buffer runs out
of data, another block of data will be read into the buffer from
the diskette.
Data is also written to diskette from the disk bufferoneblockata
time. Information that is to be transferred to disk is first sent to
the disk buffer. When the disk buffer has been filled, Atari DOS
writes the data in the buffer to the diskette.
Booting DOS
Before Atari DOS is available for usage, it must be loaded into
memory from a diskette. This process is known as booting DOS.
The procedure for booting DOS is as follows:
1. Power on Drive 1. If your system includes more than one
drive, Drive 1 can be determined by examining the access
hole on the back of each drive. On Drive 1, both the black
and white switches are located to the far left.
2. Insert a diskette containing a copy of DOS into Drive 1.
3. Turn the Atari 400 or 800's power off (if necessary) and on.
4. If you are booting DOS version 1.0 or if you are booting
DOS version 2.0 on a system without a BASIC ROM
cartridge installed, the DOS Menu will appear on the video
display.
218 User's Handbook to the Atari 400/800 Computers
5. If you are booting DOS version 2.0on a system with a BASIC
ROM cartridge installed, the BASIC prompt READY will
appear on the video display. By entering the following
command at the keyboard,
DOS /
the DOS Menu will be loaded.
In step 5, DOS. SYS is loaded during the initial part of the loading
process. When the DOS statement is executed, DUP.SYS will be
loaded into memory.
In DOS version 2.0, DUP.SYS is loaded into an area of memory
where BASIC programs are stored. When DUP.SYSis loaded, any
existing BASIC program in memory will be erased.
In DOS version 1.0 the disk utility package is contained in the
DOS. SYS file. DOS. SYS does not overwrite the area in RAM
where BASIC programs are stored. Therefore, loading DOS
version 1.0 will not affect a BASIC program in memory.
DOS Menu
The DOS Menu loaded depends on the version of DOS used.
The DOS Menu loaded by DOS version 1.0 is depicted in
Illustration 7-7 . The DOS Menu loaded by DOS version 2.0 is
pictured in Illustration 7-8.
Atari 810 Disk Drive 219
Illustration 7-7. DOS Version 1.0 Menu
DISK OPERATING SYSTEM
COPYRIGHT 1979 ATARI
9/24/79
A.
DISK DIRECTORY
I.
FORMAT DISK
B.
RUN CARTRIDGE
J-
DUPLICATE DISK
C.
COPY FILE
K.
BINARY SAVE
D.
DELETE FILE(S)
L.
BINARY LOAD
E.
RENAME FILE
M
. RUN AT ADDRESS
F.
LOCK FILE
N.
DEFINE DEVICE*
G.
UNLOCK FILE
O
DUPLICATE FILE
H.
WRITE DOS FILE
SELECT ITEM
"N-DEFINE DEVICE is not used.
Illustration 7-8. DOS Version 2.0 Menu
DISK OPERATING SYSTEM II VERSION 2.0S
COPYRIGHT 1980 ATARI
A. DISK DIRECTORY
B. RUN CARTRIDGE
C. COPY FILE
D. DELETE FILE(S)
E. RENAME FILE
F. LOCK FILE
G. UNLOCK FILE
H. WRITE DOS FILES
SELECT ITEM OR [RETURN]
I. FORMAT DISK
J. DUPLICATE DISK
K. BINARY LOAD
L. BINARY LOAD
M. RUN AT ADDRESS
N. CREATE MEM.SAV
O. DUPLICATE FILE
FOR MENU
V
220 User's Handbook to the Atari 400/800 Computers
As shown in Illustrations 7-7 and 7-8, a number of different disk
operations are available on the DOS Menu. To choose an
operation from the DOS Menu, enter the letter corresponding
to that operation and press Return.
Once the disk operation has been chosen, a prompt message for
that operation will appear on the screen. Generally, this prompt
message specifies some additional information required by the
disk operation.
Once the disk operation has been chosen, the prompt,
SELECT ITEM (DOS 1.0)
or
SELECT ITEM OR [RETURN] FOR MENU
will once again appear on the bottom of the video display.
If another item is specified, that disk operation's prompt will be
displayed. If Return is pressed, the DOS Menu will be
redisplayed.
DOS MENU OPERATIONS
In the following sections, we will discuss the various DOS Menu
Operations.
A. Disk Directory
The Disk Directory operation lists the files present on a diskette.
When the Disk Directory operation has been specified by
entering A and pressing Return, the following prompt will
appear on the video display:
DIRECTORY— SEARCH SPEC, LIST FILE
If the Return key is pressed in response to this prompt, the names
Atari 810 Disk Drive 221
of each file on the diskette in drive 1 will be displayed on the
screen followed by the size of the file (in sectors). The last line of
the directory listing will contain the number of unused sectors
on the diskette. A sample directory listing is pictured in
Illustration 7-9.
As previously mentioned, pressing Return in response to the
SEARCH SPEC, LIST FILE prompt will cause all files on the diskette
in drive 1 to be listed. When Return is pressed in response to this
prompt, DOS will assume the default values for the SEARCH
SPEC and LIST FILE parameters.
SEARCH SPEC indicates the file specification of any specific files
to be listed by the Directory operation. This file specification
consists of the capital letter D followed by the number of the disk
drive whose diskette is to be searched, followed by the name of
the file or files to be searched for. The drive identifier and
filename should be separated by a semicolon.
Illustration 7-9. Directory Listing
*DOS
SYS
039
*DUP
SYS
042
DISP
OBJ
001
PROGRAM2
BAS
012
PROGRAM3
BAS
013
600 FREE SECTORS
222 User's Handbook to the Atari 400/800 Computers
If the drive number is omitted, DOS will assume drive 1 is to be
searched. In other words D1 is the default value for the drive
identifier.
Filename match characters can be used in the filename portion
of the SEARCH SPEC parameter. For instance, the following
entry,
D2:*.DAT
would cause all files on drive 2 with the filename extension DAT
to be listed. The default value for the filename portion of the
SEARCH SPEC parameter is *.*. This value causes all files to be
listed, as *.* matches all filenames.
The second disk directory parameter, LIST FILE, specifies the
device where the directory output is to be listed. The default
value for the output device is E:, which indicates the video
screen.
If you wish to have the directory listing sent to the printer, use P:
as the LIST FILE parameter. For example, the following entry,
D2:*.DAT,P:
would cause all files on drive 2 with the extension DAT to be
listed by the printer.
When using the LIST FILE option, be certain to separate your
entry from the SEARCH SPEC entry with a comma.
B. Run Cartridge
When the Run Cartridge operation is chosen from the DOS
Menu, DOS will return control of the Atari computer to the
cartridge inserted in the unit. If the BASIC cartridge is inserted,
the BASIC prompt,
READY
will be displayed on the screen. If the Assembler Editor cartridge
Atari 810 Disk Drive 223
is inserted, the prompt,
EDIT
will be displayed.
If a cartridge is not inserted in the Atari, the following message,
NO CARTRIDGE
will appear on the screen when the Run Cartridge operation is
chosen. Another operation must then be chosen from the DOS
Menu.
If you are using DOS version 2.0, the Run Cartridge operation
should not be used to return to BASIC when the MEM. SAV file
exists on the diskette. Instead, the System Reset key should be
pressed to return to BASIC. By following this procedure, data will
be correctly returned into memory from MEM. SAV. MEM. SAV
will be discussed in more detail later in this chapter.
C. Copy File
The Copy File disk operation is used on Atari systems with two or
more disk drives to copy a file from the diskette in one drive to a
diskette in another drive. Copy File can also be used to create a
back-up copy of a file on the same diskette with a different
filename.
When Copy File is executed, the following prompt will appear
on the video display:
COPY-FROM, TO?
The FROM parameter specifies the file or files to be copied. The
FROM parameter generally consists of a file specification, but
can also be a device name such as the video screen (E:).
Filename match characters can be used in the file specification
used for the FROM parameter.
224 User's Handbook to the Atari 400/800 Computers
The TO parameter specifies the destination of the file or files
being copied. Again, the TO parameter generally consists of a
file specification, but can also be a device such as the printer (P:),
screen (E:), or disk drive (D:).
The Copy File operation cannot be used to copy the DOS. SYS
file. Any attempt to do so will result in an error message. The
DOS. SYS file can be copied using the Write DOS.SYS operation
(H.).
If the source file specified does not exist, error 170 (FILE NOT
FOUND) will appear on the screen. If the destination diskette's
directory already contains 64 filenames, error 169 (DIRECTORY
FULL) will appear. If there are not enough free sectors on the
destination diskette for the copy operation to take place, error
162 (DISK FULL) will appear.
If you are using the Copy File operation in DOS version 2.0 and a
MEM.SAV file exists on the system diskette, a second prompt
message (as shown below) will appear before the Copy File
operation is executed.*
TYPE "Y" IF OK TO USE PROGRAM AREA
CAUTION: A "Y" INVALIDATES MEM.SAV
If the user's response to the preceding prompt is Y, Copy File will
use the entire user program area for the copying process which
invalidates the MEM.SAV file.
A response of N instructs DOS to use a smaller internal buffer for
the Copy Files operation. The MEM.SAV file will be retained.
However, the copying process will be slower.
The Copy File operation can be used with the Append option
(/A) to add one file to the end of another file. This process is
known as merging.
For example, the following parameter entry would cause
FILEA.TXT to be merged with FILEB.TXT.
•This prompl may nol appear in some systems.
Atari 810 Disk Drive 225
COPY--FROM, TO?
D1:FILEA.TXT, D2.-FILEB.TXT/ A
The Append option should not be used with BASIC program files
stored in tokenized format.
Illustration 7-10 contains examples of the usage of the Copy File
operation.
Illustration 7-10. Copy Files Example
Example 1
SELECT ITEM OR [RETURN] FOR MENU
COPY--FROM, TO?
D1:FILEA.TXT, D2:FILEA.TXT /
SELECT ITEM OR [RETURN] FOR MENU
In the preceding example, FILEA.TXT is copied from the diskette
in drive 1 to the diskette in drive 2, using the same filename.
Example 2
SELECT ITEM OR [RETURN] FOR MENU
COPY--FROM, TO?
D1:FILEA.TXT, D1:FILEB.TXT /
SELECT ITEM OR [RETURN] FOR MENU
226 User's Handbook to the Atari 400/800 Computers
In Example 2, a copy of FILEA.TXT is created on the diskette in
drive 1 and is assigned a new filename FILEB.TXT.
Example 3
SELECT ITEM OR [RETURN] FOR MENU
COPY-FROM, TO?
D1:PROGA.BAS,P: /
SELECT ITEM OR [RETURN] FOR MENU
In Example 3, PROGA.BAS is listed on the printer.
Example 4
SELECT ITEM OR [RETURN] FOR MENU
COPY— FROM, TO?
E:, D1.TEXTC.DAT /
PEAR/
APPLE >
BANANA >
GRAPES /
Control-3
SELECT ITEM OR [RETURN] FOR MENU
In Example 4, the data displayed on the screen will be copied into
TEXTC.DAT on drive 1. When Control-3 is pressed, the entry will
be ended.
Atari 810 Disk Drive 227
D. Delete File
The Delete File operation allows the user to delete unneeded
files from the diskette and the disk directory.
When the Delete File operation is chosen, the following prompt
will appear on the video display.
DELETE FILESPEC
The file specification should be entered. Filename match
characters may be used in the file specification.
Once the file specification has been entered, a second prompt
will be displayed.
TYPE "Y" TO DELETE...
FILENAME
FILENAME will be replaced with the filename of the file to be
deleted. If the user enters Y followed by Return, the file will be
deleted. If N or any other letter is entered followed by Return,
the file will not be deleted.
If the file specification entered in response to the DELETE
FILESPEC prompt matches more than one filename on the
diskette, each matching filename will be displayed. The user
must enter Y following each filename for the deletion to occur.
If the No verification option (/N) is specified in response to the
DELETE FILESPEC prompt, the second prompt will not appear,
The files specified will automatically be deleted.
A file which has been locked cannot be deleted using the Delete
File operation. Any attempt to do so will result in error 167,
Examples of the use of the Delete File operation are given in
Illustration 7-11.
228 User's Handbook to the Atari 400/800 Computers
Illustration 7-11. Delete File Example
Example 1
SELECT ITEM OR [RETURN] FOR MENU
D/
DELETE FILESPEC
D1:*.TXT^
TYPE "Y" TO DELETE...
D1iFILEA.TXT
1/
D1:FILEB.TXT
1/
SELECT ITEM OR [RETURN] FOR MENU
In the preceding example, any files with an extension of .TXT will
be prompted for deletion. FILEA.TXT and FILEB.TXT will both be
deleted from the diskette in drive 1.
Example 2
SELECT ITEM OR [RETURN] FOR MENU
DELETE FILESPEC
*.VN >
SELECT ITEM OR [RETURN] FOR MENU
In Example 2, all files on the diskette in drive 1 will be deleted.
Note the use of the No Verification option to suppress the
second prompt.
E. Rename File
The Rename File operation can be used to change the name of
any file on the diskette. Be careful not be use Rename File to
Atari 810 Disk Drive 229
change the name of DOS. SYS. If DOS.SYS is renamed, the DOS
menu will no longer load.
When Rename File is specified, the following prompt will
appear.
RENAME, GIVE OLD NAME, NEW
OLD NAME will consist of the file specification of the file to be
renamed. If a drive identifier is not included in the file
specification, drive 1 will be assumed.
The NEW NAME will consist of the new filename for the file
specified in OLD NAME. Filename match characterscan be used
with both the OLD NAME and NEW NAME parameters.
A locked file cannot be renamed. Any attempt to do so will result
in error 167 (File Locked).
A file on a diskette that has been write-protected cannot be
renamed. Any attempt to do so will result in error 144 (Device
Done Error).
Also, if the user attempts to rename a file that does not exist on
the diskette, error 170 will occur (File Not Found).
Examples of the use of the Rename File operation are given in
Illustration 7-12.
230 User's Handbook to the Atari 400/800 Computers
Illustration 7-12. Rename File Examples
Example 1
SELECT ITEM OR [RETURN] FOR MENU
RENAME-GIVE OLD NAME, NEW
TEXTA.DAT, TEXTB.DAT ^
SELECT ITEM OR [RETURN] FOR MENU
In Example 1, TEXTA.DAT on drive 1 is renamed to TEXTB.DAT.
Example 2
SELECT ITEM OR [RETURN] FOR MENU
RENAME--GIVE OLD NAME, NEW
D2:*.BAS,*.BAK ^
SELECT ITEM OR [RETURN] FOR MENU
In Example 2, all files on drive 2 with the extension .BAS will be
renamed with the extension .BAK.
F. Lock File
The Lock File operation write protects a file. When a file is
locked, it cannot be written to, renamed, deleted, or appended
to. If an attempt is made to do so, error 167 (File Locked) will
appear.
Atari 810 Disk Drive 231
Locked files appear in the Disk Directory with an asterisk before
the filename.
When the Lock File operation is specified, the following prompt
will appear.
WHAT FILE TO LOCK?
Enter the file specification of the file to be locked. Filename
match characters may be used to lock multiple files with a single
file specification.
It is good practice to lock the DOS. SYS and DUP.SYS files.
G. Unlock File
The Unlock File operation is used to unlock one or more disk
files previously locked with Lock File. When the Unlock File
operation is specified, the following prompt will appear:
WHAT FILE TO UNLOCK?
The file specification of the file to be unlocked should be
entered. Filename match characters can be used to specify more
than one file.
H. Write DOS File
The Write DOS File operation allows the user to copy DOS 1.0 or
2.0 onto a diskette. In DOS version 1.0, the DOS.SYS file is
copied. In DOS version 2.0, the DOS.SYS and DUP.SYS files are
copied.
DOS is copied from the computer's memory, not directly from a
diskette during the Write DOS File operation.
In DOS 1.0, the following prompt appears when Write DOS File
is specified.
TYPE "Y" TO WRITE NEW DOS FILE
232 User's Handbook to the Atari 400/800 Computers
DOS.SYS will be written to the diskette in drive 1.
In DOS 2.0, the following prompt will appear.
DRIVE TO WRITE FILES TO?
Here, the operator should enter the drive number where DOS
should be copied. This can be either drive 1, 2, 3, or 4. Once the
drive number has been entered, the following prompt will
appear.
TYPE "Y" TO WRITE NEW DOS FILE
If a Y is entered, DOS will be written to the diskette in the
specified drive. Any other entry aborts the Write DOS File
operation.
I. Format Diskette
All blank diskettes must be formatted before they can be used by
DOS. Formatting is a process where a pattern is recorded on the
diskette which allows data to be written to or read from its
surface. The Atari 810 Disk Drive requires approximately two
minutes to format a diskette.
When the Format Diskette operation is specified, the following
prompt will appear.
WHICH DRIVE TO FORMAT?
The user should specify the number of the drive containing the
diskette to be formatted. A second prompt will then appear.
TYPE "Y" TO FORMAT DRIVE 1*
If the user responds to this prompt with a Y, the diskette in the
drive specified will be formatted. Any other entry will abort the
Format Diskette operation.
♦assuming drive 1 was specified in the first prompt.
Atari 810 Disk Drive 233
If a diskette contains bad sectors, DOS will not format it. After
the initial discovery that the diskette contains bad sectors, DOS
will attempt to format the diskette two more times. Upon the
third unsuccessful attempt, error 173 (Bad Sectors at Format
Time) will be displayed.
Be certain that you do not format a diskette that contains data
you wish to retain. Formatting a diskette destroys any existing
data on that diskette.
J. Duplicate Disk
The Duplicate Disk operation allows an entire diskette to be
copied. This operation can be used with Atari systems with either
one or two disk drives.
When Duplicate Disk is specified, the following prompt will
appear.
DUP DISK-SOURCE, DEST DRIVES?
The user should respond with the drive number containing the
diskette to be copied, and the drive number which will contain
the diskette in which the copy is to be made.
If your Atari system has only one drive, you should respond to
this prompt with an entry of 1,1.
The following prompt will then be displayed.
INSERT SOURCE DISK, TYPE RETURN
The user should then insert the diskette to be copied in the sole
disk drive and press Return. A portion of the data stored on the
diskette will then be read into the Atari's memory. The following
prompt will then be displayed.
INSERT DESTINATION DISK, TYPE RETURN
The user should then replace the diskette being copied with a
blank formatted diskette and press Return.
234 User's Handbook to the Atari 400/800 Computers
The data held in the Atari's RAM will be written to the
destination diskette, after which the Insert Source Disk prompt
will reappear. Continue this process until the entire diskette has
been copied.
If your Atari system contains multiple drives, the duplication
process is much more simple. When different source and
destination drives are specified (ex. 1,2), the following prompt
will be displayed.
INSERT BOTH DISKETTES, TYPE RETURN
After inserting the diskette to be copied in the source drive and
the blank diskette on which the copy is to be made in the
destination drive, press Return and the duplication process will
begin. The duplication process can take several minutes if the
source file is filled.
It is a good practice to write protect the source diskette to
prevent it from being accidentally overwritten if an error is
made.
With DOS version 2.0 systems, the following prompt is
displayed.*
TYPE "Y" IF OK TO USE PROGRAM AREA?
CAUTION: A "Y" INVALIDATES MEM.SAV
If Y is entered, the user program area will be used for the copying
process, and existing programs in memory will be erased. An
entry other than Y causes Duplicate Disk to be aborted. If a
program is stored in RAM that you wish to save, it should be
copied to cassette or diskette before the Duplicate Disk
operation is begun.
K. Binary Save
The Binary Save operation is used to save the contents of RAM
on disk in object file format. This format is also used for programs
written using the Assembler Editor cartridge.
When the Binary Save operation is specified in DOS 2.0, the
•This prompt may nol appear in some systems.
Atari 810 Disk Drive 235
following prompt will be displayed.
SAVE-GIVE FILE, START, END (,INIT, RUN)
FILE is the name of the file to be saved. A drive specifier may be
included.
The START and END parameters are required for either a binary
file or a program. These specify the starting and ending
addresses in hexadecimal of the portion of the memory to be
saved.
The I NIT and RUN addresses are optional parameters. These
allow a program to be executed upon loading. The INIT address
gives the starting address of an initialization routine. The RUN
address gives the starting location of the main program. The INIT
and RUN addresses are used by the Binary Load operation to
automatically execute a program after it has been loaded. The
INIT and RUN addresses must be specified in hexadecimal
notation.
When the Binary Save operation is specified in DOS 1.0, the
following prompt will appear.
SAVE--GIVE FILE, START, END
Again, FILE gives the name of the object file to be created. A
drive specifier can be used preceding the filename.
START and END give the beginning and ending addresses in
hexadecimal of the block of data to be saved.
A file can be saved in DOS 1.0 so that it will be automatically
executed when it is loaded by Binary Load. To accomplish this,
the program starting address should be placed in memory
addresses 736 and 737 (2E0 and 2E1 in hexadecimal). The low byte
of the program starting address should be placed in address 736
and the high byte in 737. The POKE statement can be used to
place the proper values in these locations.
Illustration 7-13 gives an example of the use of the Binary Save
236 User's Handbook to the Atari 400/800 Computers
operation.
Illustration 7-13. Binary Save Example
SELECT ITEM OR [RETURN] FOR MENU
SAVE-GIVE FILE, START, END (,INIT, RUN)
FILEA.OBJ, 2B00, 4C0F ^
SELECT ITEM OR [RETURN] FOR MENU
In the preceding example, the contents of memory locations
beginning at 2B00 and ending at 4C0F will be saved in a file
named FILEA.OBJ on drive 1.
L. Binary Load
The Binary Load operation is used to load a file created with
Binary Save or an assembly language object file into RAM. If the
RUN and INIT addresses were appended to the file, the file will
execute upon loading.
If the /N option is specified, the INIT and RUN addresses will be
disregarded, and the file must be run using the DOS Menu's Run
At Address operation. Also, files without an INIT or RUN address
must be run using the Run At Address operation.
An example of a Binary Load operation is given in Illustration 7-
14.
Atari 810 Disk Drive 237
Illustration 7-14. Binary Load Example
SELECT ITEM OR [RETURN] FOR MENU
LOAD FROM WHAT FILE?
FILEA.OBJ /
SELECT ITEM OR [RETURN] FOR MENU
In some situations in DOS 2.0, the binary file may require a
portion of the memory area used by DUP.SYS. If this occurs, the
portion of the binary file that requires memory used by DUP.SYS
will be saved on the MEM.SAV file until the binary file has been
executed. If the MEM.SAV file is not present, the following
message will appear.
NEED MEM.SAV TO LOAD FILE
M. Run At Address
The Run At Address operation is used to execute a machine
language program in memory by entering its hexadecimal
starting address. An example of the use of the Run At Address
operation is given in Illustration 7-15.
238 User's Handbook to the Atari 400/800 Computers
Illustration 7-15. Run At Address Example
SELECT ITEM OR [RETURN] FOR MENU
M/
RUN FROM WHAT ADDRESS
2B00 /
N. Create MEM.SAV*
The Create MEM.SAV operation is used to create a MEM.SAV file
on the diskette in drive 1.
Whenever DOS version 2.0 is booted, the DUP.SYS disk file will
overwrite an area in memory where BASIC programs are stored.
When a MEM.SAV file is present on the diskette in drive 1, the
computer will transfer all data present in the memory area used
by DUP.SYS into the MEM.SAV file. Afterwards, DUP.SYS will be
loaded, and the DOS menu will appear.
When you have finished using DOS, by entering the
Run Cartridge operation, the program in MEM.SAV will be
automatically loaded from MEM.SAV into RAM.
When a MEM.SAV file is used, more time will be required to load
the DOS menu. Illustration 7-16 depicts the use of Create
MEM.SAV.
*Define Device (Item N. in DOS version 1.0) is not utilized.
Atari 810 Disk Drive 239
Illustration 7-17. Create MEM.SAV Example
SELECT ITEM OR [RETURN] FOR MENU
TYPE "Y" TO CREATE MEM.SAV
1/
SELECT ITEM OR [RETURN] FOR MENU
If the user attempts to create a MEM.SAV file on a diskette which
already contains a MEM.SAV file, the following will be displayed
on the video screen.
MEM.SAV FILE ALREADY EXISTS
SELECT ITEM OR RETURN FOR MENU
O. Duplicate File
The Duplicate File operation is used to copy file from one
diskette to another in systems with only one drive.
When the Duplicate File operation is specified, the following
prompt will appear.
NAME OF FILE TO MOVE?
Since the source and destination files will be the same, only one
filename need be entered. Also, since the system includes only
one disk drive, a drive identifier is not necessary. Filename match
characters may be used in the filename entry.
In DOS version 2.0, the following prompt will then appear.*
TYPE "Y" IF OK TO USE PROGRAM AREA
CAUTION: A "Y" INVALIDATES MEM.SAV
"This prompt may not appear in some systems.
240 User's Handbook to the Atari 400/800 Computers
If a Y is entered, the entire program area of memory will be used
for the file duplication process. This will speed the duplication
process. However, by allowing the program area to be used for
duplication, the contents of MEM.SAV cannot be rewritten into
RAM. Any BASIC program that you intended to save using
MEM.SAV will be lost when the system returns to BASIC.
Any response other than Y disallows the use of the program area
of memory for the Duplicate File operation. This allows the
contents of MEM.SAV to be later rewritten into RAM. However,
by disallowing the use of the program area of memory, the time
necessary to duplicate the file will increase.
Be extremely careful when using the Duplicate File operation
with DOS 1.0. When this operation is specified in DOS 1.0, the
program area of memory will be erased. Any existing files will be
lost after the duplication process has been completed.
An example of the use of the Duplicate File option is given in
Illustration 7-18. Notice that the diskettes may have to be
swapped several times in order to complete the duplication
process.
USING BASIC PROGRAMS ON DISKETTE
In the following sections, we will discuss the BASIC statements
used to save programs on diskette and then reload these
programs back into memory.
Saving BASIC Programs On Diskette
Once a BASIC program has been entered into RAM via the
keyboard, it must be stored on diskette or it will be lost when the
Atari's power is turned off or when a NEW statement is executed.
The SAVE and LIST statements are used to save a BASIC program
on diskette.
The SAVE statement uses the followng configuration when used
with the Atari 810 Disk Drive.
Atari 810 Disk Drive 241
Illustration 7-18. Duplicate File Example
SELECT ITEM OR [RETURN] FOR MENU
O/
NAME OF FILE TO MOVE?
TEXT?. DAT >
TYPE "Y" IF OK TO USE PROGRAM AREA
CAUTION: A "Y" INVALIDATES MEM.SAV
1/
INSERT SOURCE DISK, TYPE RETURN
/
COPYING-D1rTEXTA.DAT*
INSERT DESTINATION DISK, TYPE RETURN
/
INSERT SOURCE DISK, TYPE RETURN
•
COPYING--D1 :TEXTB.DAT*
INSERT DESTINATION DISK, TYPE RETURN
•
INSERT SOURCE DISK, TYPE RETURN
SELECT ITEM OR [RETURN] FOR MENU
This message appears only if more than one file is copied.
SAVE "D#:filename"
where D is the device name for the Atari 810 disk drive. This
parameter is required. # indicates the drive number (1,2, 3, or 4).
If # is omitted, drive 1 is assumed. The BASIC program filename is
separated by a colon from the device name and drive number.
The SAVE statement stores BASIC programs in tokenized format,
keywords are abbreviated as one character tokens.
242 User's Handbook to the Atari 400/800 Computers
The LIST statement uses the following configuration,
LIST "D#:filename"[,beginline][endHne]*
where D specifies the device name. # is an optional parameter
which specifies the drive number. The filename assigned to the
file is specified in filename.
beginline and endline are optional parameters which specify the
first and last line numbers to be stored by LIST. All line numbers
with values between beginline and endline will be stored as well.
For example, the following LIST statement would save all
program lines between 100 and 500 inclusive on the diskette in
drive 2 with the filename PROGA.BAS:
LIST "D2:PROGA.BAS", 100, 500
The LIST statement saves programs in Atari ASCII format. In this
format, every character is assigned an ASCII code.
Loading a Program
The LOAD statement is used to load programs into memory from
diskette which were previously saved in tokenized format by the
SAVE statement.
The LOAD statement uses the same format as the SAVE
statement. The following LOAD statement would load
PROGA.BAS from drive 1:
LOAD "D: PROGA.BAS"
The ENTER statement is used to load a program previously saved
in ASCII format with a LIST statement. The following ENTER
statement would load PROGB.BAS from drive 1:
ENTER "D:PROGB.BAS"
'Brackets [] indicate an optional entry.
Atari 810 Disk Drive 243
If the program file specified by ENTER or LOAD is present on the
specified drive, it will be loaded into memory. When the loading
process has been completed, the READY prompt will be
displayed.
If the program specified by ENTER or LOAD is not present on the
drive indicated, error 170 (File Not Found) will occur.
The LOAD statement will erase any existing program in memory
when the new program is loaded. The ENTER statement merges
the program being loaded with any existing program lines in
memory. If the program being loaded contains line numbers
which duplicate those of the program in memory, the incoming
program lines will replace the duplicate lines in memory. Any
existing program lines in memory can be erased by entering the
NEW statement before executing an ENTER statement.
LOADing and Executing a Program
In the following series of statements, a BASIC program is loaded
with the LOAD statement, and then executed with the RUN
statement.
LOAD "D:PROGA.BAS"
READY
RUN
This process can be shortened to a single step by including the
LOAD statement's parameter with the RUN statement. An
example of this usage of the RUN statement is given below.
RUN "D:PROGA.BAS"
In the preceding example, PROGA.BAS will be executed as soon
as it is loaded.
Chaining Programs
The RUN statement can be included as a program line in one
program in order to load and execute another program. This
process is known as chaining.
244 User's Handbook to the Atari 400/800 Computers
For example, when the following program is executed, line 500
will cause a second program (PROCB.BAS) to be executed.
100 REM PROGA.BAS
200 A = 9: B = 10
300 C = A * B
400 PRINT C
500 RUN "D:PROGB.BAS"
When the new program is loaded in line 500, all variable values
will be cleared before PROGB.BAS is loaded. This is due to the
fact that the RUN statement as used in line 500 executes a LOAD
statement. The LOAD statement in turn executes a NEW
statement which erases any existing programs in memory and
clears all variables.
USING DATA FILES ON DISKETTE
The BASIC statements PRINT#and PUT are used to store data on
a diskette. INPUT# and GET are used to read data into RAM from
a diskette.
Opening a Disk File
Before a disk file can be used, it must first be opened with the
OPEN statement. The OPEN statement will open an
input/output channel to the file specified as its parameter. The
OPEN statement uses the following configuration:
OPEN ^channel, task, value, D#:filename
The first parameter in the OPEN statement indicates the channel.
Before an external device can be accessed either for input or
output, a channel to the device must have been opened.
The OPEN statement assigns a channel to an external device.
Once a channel is assigned, the device can subsequently be
accessed via its channel number. If an OPEN statement attempts
to open a channel which is already open, an error will occur.
Atari 810 Disk Drive 245
The second parameter in the OPEN statement indicates the
activity for which the channel is being opened. The activities
which can be specified for the Atari 810 Disk Drive are listed in
Table 7-1.
The third parameter in the OPEN statement is ignored when the
Atari 810 is specified as the device. A value of should be used.
The final parameter in the OPEN statement consists of the device
name for the Atari 810 Disk Drive (D), followed by an optional
drive specifier, and the name of the file to be opened.
Table 7-1. OPEN Statement Task Parameter Values
(Atari 810 Disk Drive)
Task Parameter
Number
Task Description
Disk read operation. The file pointer is
positioned to the beginning of the file.
Disk directory read operation. This
operation allows the user to read the
disk directory as if it was a data file. The
file pointer will be set to the first
filename in the directory that matches
the specified filename.
When the disk directory file is read, the
fields containing filenames which match
the filename specified in the OPEN
statement will be returned. Filenames
that do not match will be skipped. The
last value that is returned is the number
of free sectors.
If the following OPEN statement was
specified;
OPEN #1,6,0,"D:*.BAS"
246 User's Handbook to the Atari 400/800 Computers
all files with an extension of .BAS would
be returned during a read operation.
Disk write operation. The file pointer is
positioned to the beginning of the file.
Any existing data in the file is erased.
Disk write append operation. The file
pointer is positioned to the end of the
file. The file must already exist or error
170 will occur. The append operation
allows data to be added to an existing
file.
Disk read and write operation. The file
pointer is positioned to the beginning of
the file, and existing data in the file is
not altered. The file must already exist
before it can be opened for updating. As
data is read or written, the file pointer
will be moved forward in the file. Data
written to the file will replace existing
data.
A file must be opened via the OPEN statement before that file
can be referenced in a program. Once a file has been opened, it
is referenced with its channel number, not with its filename.
Channels 1 to 5 are always available for use in Atari BASIC
programs. Channel is reserved for the editor (E:). The BASIC
graphics statements use channel 6. The CLOAD, CSAVE, and
LPRINT statements use channel 7. As long as the BASIC program
does not use the graphics statements, channel 6 will be available
for use. If CLOAD, CSAVE, and LPRINT are not used, channel 7
will be available.
Closing a Data File
Once a program has finished accessing an open file, that file
should be closed with the CLOSE statement. This allows that file's
Atari 810 Disk Drive 247
channel number to be assigned elsewhere.
Also, if a file that was open for output is not properly closed, data
may be lost. Closing an output file causes any remaining data in
the disk drive buffer to be output followed by an end-of-file
record. If the open file is not properly closed, the data in the disk
drive buffer may be lost.
The following CLOSE statement,
CLOSE #4
will close channel 4.
All open files are closed automatically when an END or RUN
statement is executed, or when a program's last statement is
executed (only in the program mode). However, it is good
programming practice to close any open files with the CLOSE
statement.
Writing to a Data File
Once a file has been opened, data can be written to that file
using the PRINT# or PUT statements.
The PRINTS statement uses the following configuration when
used to output data to a disk file.
PRINT ^channel; expression
channel indicates the channel to be used to send the output.
Use the channel assigned to the file in the OPEN statement.
expression consist of one or more string or numeric values to be
output. These values are output as ASCII values.
Data is output to the disk drive via the disk drive buffer. The disk
drive buffer stores data output from PRINT# statements until the
buffer fills or an end-of-line character is encountered.
The disk drive buffer has a capacity of 125 characters. Therefore,
data will be output from the buffer to the diskette in 125
248 User's Handbook to the Atari 400/800 Computers
character blocks. If an EOL character is output, the disk buffer
contents will be sent to the diskette regardless of whether or not
the buffer is filled. If a PRINT# statement contains more than one
expression, these will be concatenated unless separated with an
EOL character.
PRINT* statements automatically output an EOL character after
outputting the expressions. However, a comma or semicolon at
the end of a PRINT# statement suppresses the EOL character.
If the previous PRINTS statement expression list ended with a
semicolon, the current PRINTS statement would output its first
character immediately after the final character that was output
by the preceding PRINTS statement. If the previous PRINTS
statement expression list ended with a comma, the current
PRINTS statement would begin output at the next column tab
stop.
Blank spaces will be placed in the area between the last character
output via PRINTS and the first character output at the next tab
stop by the current PRINTS statement. Because of the insertion
of these blank spaces, it is advisable not to insert commas in
PRINTS statements used for disk output.
The PUT statement can also be used to output data to a disk file.
PUT takes the following configuration:
PUT #channel, numeric expression
As with PRINTS, the channel specified must be open for output.
The value given in numeric expression is output to the data file.
The value output will lie between Oand 255. If the value is not an
integer, it will be rounded to the nearest integer.
If the value specified does not lie between and 255, it will be
output module 256. In other words, 256 would be sent as 0,257 as
1, 258 as 2, 259 as 3, etc.
Reading From a Data File
The INPUTS and GET statements are used to read data from files
Atari 810 Disk Drive 249
and assign that data to the variables specified in the statement.
INPUT# uses the following configuration:
INPUT #channel \ ! I variable,...
{;)
The channel must have been previously opened for input. The
variables will accept the data values input.
INPUT* will retrieve data from the input device specified. This
data will consist of ASCII characters followed by the ASCII end-
of-line character. The EOL character will end input to the
variable specified.
INPUT# will interpret the data being read as either numeric or
string— depending on the type of variables used as parameters.
When a numeric variable is specified, the data being input will
be interpreted as numeric data.
The data read via INPUT* will be assigned to the numeric
variable indicated until a comma or an EOL character is
encountered. Numeric values can be ended either with the EOL
character or comma. Commas can not be used to end string
values, as they are regarded as part of the string.
If no data is available to be read into the numeric variable, or if
the data is invalid, an error will result.
When a string variable is specified, the data being input will be
interpreted as string data. If no characters are read, the string
variable will be assigned the null value. If more characters are
read than allowed for in the string variable's DIM statement, the
INPUT* statement will disregard the excess characters. The EOL
character will end the string input.
The INPUT* statement transfers data from the diskette in 125
character blocks. A single block might contain values which will
be assigned to several variables. The variables specified in the
INPUT* statement will be assigned the values in the disk buffer in
a sequential manner.
250 User's Handbook to the Atari 400/800 Computers
If an INPUT* statement attempts to read beyond the end of a disk
file, an error will result.
The GET statement is used to read a single numeric value via the
open channel specified. GET uses the following configuration:
GET #channel, numeric variable
The channel specified must be open for input. The numeric
variable indicated will accept the value returned by GET. This
value will lie between and 255.
When GET is used with the 810 Disk Drive and the buffer is
empty, the initial GET statement will result in a block of data
being read into the disk buffer. The first value in the buffer will
be assigned to the numeric variable specified with the first GET
statement.
Each successive GET statement will read a value from the buffer.
When the buffer has been emptied, another block of data will be
read into the buffer from the diskette.
NOTE and POINT
NOTE and POINT are BASIC statements that aid the user in
random access of Atari disk files. Random access is only possible
with DOS version 2.0.
The NOTE statement will return the position of the file pointer.
The file pointer will be referenced using two separate data items.
One data item is the number of the last sector accessed. The
other data item is the number of the last character referenced
within that sector.
The NOTE statement uses the following configuration:
NOTE #channel, sector, character
The NOTE statement will reference the file opened with the
specified channel number. The number of the last sector
accessed will be assigned to the variable given in sector. The
Atari 810 Disk Drive 251
number of the last character accessed within that sector will be
assigned to the variable named in character.
The sector number returned is the absolute sector number on
the diskette. It can be any number from 1 to 719. Remember, a
file's sector numbers need not necessarily be sequential. For
example, the first sector for a file might be sector 57, the second
147, the third 32, etc.
The POINT statement moves the file pointer to the sector and
character number specified. Any subsequent file access will
begin at the new file pointer location specified by POINT.
POINT uses the following configuration:
POINT ^channel, sector, character
The file open under the channel number specified will have its
file pointer moved. The file pointer will be moved to the sector
number indicated in sector, and the character within that sector
indicated by character. Both sector and character must be
numeric variables. Constants may not be used.
If the file pointer is moved to a sector not assigned to the file
opened under the channel number specified in channel, one of
the following errors will result when an attempt is made to read
from or write to that file.
Error 170 (End of File)— Attempted read.
Error 171 (Point lnvalid)~Attempted write.
CHAPTER 8.
ATARI PRINTERS
Introduction
In this chapter, we will concentrate on sending output to the
three Atari printers; the Atari 820 Printer, the Atari 822 Printer,
and the Atari 825 Printer.
The process of outputting numbers and text differs only slightly
between these three printers. However, the Atari 825 has several
programmable features not available on the Atari 820 and 822.
These will be described at the end of this chapter.
Another difference between the three Atari printers lies in the
width of the lines they output. The Atari 820 and 822 output 40
column lines. This is the same output width as the video display.
On the other hand, the Atari 825 generally uses a line width of 80
columns.
One final difference lies in the way in which these three printers
are connected to the Atari computer. The Atari 820 and 822 are
connected to the Atari computer via the serial I/O port. The
Atari 825 printer is connected to the Atari 400 or 800 via the Atari
850 Interface module.
BASIC STATEMENTS FOR PRINTER OUTPUT
Sending output to the printer is generally much the same as
sending output to the screen. In the following sections, we will
discuss the procedures to output data to the printer.
LIST '?-."
When used with the printer's device name (P:), the LIST
statement will output the BASIC program currently in memory
254 User's Handbook to the Atari 400/800 Computers
to the printer. One or two optional line numbers may also be
used as parameters to output only a portion of the program.
When a program is listed to the Atari 820 or 822, the individual
lines will have a maximum width of 40 columns. Program lines
greater than 40 characters in length will be continued on the
next line. Since the Atari 825 has an 80 column width, only
program lines greater than 80 characters will be continued on
the next line.
None of the Atari printers can output the graphics characters.
On the Atari 820 and 822, graphics characters will appear as blank
spaces. On the Atari 825, certain graphics characters cause
abnormal output while other graphics characters do not print at
all.
The Atari 825 uses certain Atari ASCII codes as printer control
characters. If the printer encounters these control characters in a
program, peculiar printer output can result. For this reason,
control codes should be specified in Atari BASIC programs using
the CHR$ function.
LPRINT
LPRINToutputs data to the printer much as the PRINTstatement
outputs data to the video display.
LPRINT is designed for use with printers using 40 column output.
This presents difficulties in situations where LPRINT is used with
the Atari 825. For example, if an LPRINT statement outputs 40
characters or less and ends with a semicolon, or 38 characters or
less and ends with a comma, the output from the next LPRINT
statement will begin on column 41 of the same line. If a third
LPRINT statement follows, output from that statement will begin
at the beginning of the next printer line.
If an LPRINT statement outputs over 40 characters on an Atari
825, the next LPRINT statement causes output to begin on a new
line— even if the statement ends with a comma or semicolon.
Atari Printers 255
On either the Atari 820, 822, or 825, if an LPRINT statement does
not end with either a comma or semicolon, output from the next
LPRINT statement will begin at the beginning of the next line.
LPRINT uses channel 7 for printer output. If channel 7 has
already been opened for another device, an error will occur
when LPRINT is executed. This error will automatically close
channel 7, after which LPRINT can be executed.
PRINT* and PUT
Either the PRINT* or PUT statements can be used to send output
to the printer. PRINT# and PUT direct output to a channel
previously opened via an OPEN statement. If the channel was
opened for the printer (device P:), the output for that channel
will be directed to the printer.
Characters are output to the printer via PRINTS and PUT in the
same manner as they are output to the display screen.
The printer must be powered on when a PRINT# or PUT
statement outputs data to the printer. If not, an error will occur.
PRINTER BUFFER
The Atari printers contain enough RAM to hold one line of
output. This memory is known as the printer buffer. As
characters are output to the printer, these are not automatically
printed but are instead sent to the printer buffer.
When either an EOL character is encountered or when the
buffer fills, an entire line will be output. The buffer will be
cleared, and the printer will advance to the next line.
PRINTER CHARACTERS SETS
The Atari printers use a character set that is somewhat different
than the character set used by the video display. The Atari
printers use the standard ASCII code set to define their character
set. The display screen uses the Atari ASCII code set. Both code
sets are listed in Appendix C.
256 User's Handbook to the Atari 400/800 Computers
Remember that none of the Atari printers are capable of
outputting the graphics characters. Also, the Atari 820 and 822
recognize ASCII codes to 31 as a blank space, while the Atari
825 recognizes these as control codes.
Atari 825 Control Characters
The Atari 825 has a number of special printing features such as
underlining, double-wide character printing, and condensed
character printing. These features are summarized in Table 8-1.
These features are activated and deactivated with control
characters. These control characters are also listed in Table 8-1.
A control character can be sent to the Atari 825 printer with the
LPRINT, PRINT#, or PUT statements just as any other character
would be sent.
Control codes can be generated either with the CHR$ function
or via the keyboard. The following program lines would cause a
reverse line feed.
100 LPRINT CHR$(27);CHR$(10)
Control characters can also be generated with the keystrokes
listed in Table 8-1. When these keystrokes are entered, the
graphics characters given in Table 8-1 will be echoed on the
screen. The screen interprets the keyboard entry as an Atari
ASCII code and displays the corresponding character on the
screen.
The Atari 825 interprets the keyboard entry as a control
character. For example, if the following line was entered,
100 LPRINT" CTRL-J " Control-J is
entered at the
keyboard
the paper would advance 1 line in the Atari 825. The graphics
character E would be displayed on the video screen.
Atari Printers 257
Table 8-1. Atari 825 Printer Control Characters
Screen
Character
Keystrokes
Decimal
Code
ASCII
Mnemonic
Atari 825
Control Functions
e
CTRL-J
10
LF
Line Feed
El IS
ESC/ESC & CTRL-J
27 & 10
ESC LF
Reverse line feed
BE
ESC/ESC & ESC/CTRL-t
27 & 28
ESC FS
Half-line feed
SB
ESC/ESC & ESC/CTRL--^
27 & 30
ESC RS
Reverse half-line feed
n
CTRL-M
13
CR
Carriage return
□
CTRL-N
14
SO
End underline
a
CTRL-O
15
SI
Begin underline
BE
ESC/ESC & CTRL-A
27 & 01
ESC SOH
1 dot space
(SO
ESC/ESC & CTRL-B
27 & 02
ESC STX
2 dot spaces
BE
ESC/ESC & CTRL-C
27 & 03
ESC ETX
3 dot spaces
SB
ESC/ESC & CTRL-D
27&04
ESC EOT
4 dot spaces
B0
ESC/ESC & CTRL-E
27 & 05
ESC ENQ
5 dot spaces
IS
ESC/ESC & CTRL-F
27&06
ESC ACK
6 dot spaces
H
CTRL-H
08
BS
Backspace. Code
must be followed
with a character.
SB
ESC/ESC & CTRL-N
27 & 14
ESC SO
Begin extended char-
acter printing.
B0
ESC/ESC & CTRL-O
27 & 15
ESC SI
End extended char-
acter printing.
SIS
ESC/ESC & CTRL-S
27 & 19
ESC DC3
Standard character
spacing. 10 character
per square inch.
EUS
ESC/ESC & CTRL-T
27 & 20
ESC DC4
Condensed charac-
ter spacing. 16.7 char-
acters per square
inch.
GQ
ESC/ESC & CTRL-Q
27 & 17
ESC DC1
Proportionally spaced
character set.
258 User's Handbook to the Atari 400/800 Computers
The preferred method of sending control codes to the Atari 825
is via the CHR$ function. If a program is listed containing control
codes specified by the CHR$ function, the listing of that program
will not affect the printer. However, if a program containing
control characters surrounded by quotation marks is listed,
those control characters will be heeded by the Atari 825, and the
program listing will be affected accordingly.
Line Feed
The line feed code will advance the paper in the Atari 825 by one
line or 1/6 of an inch.
Any data received prior to the line feed code will be printed
before the paper is advanced. The following statement,
100 LPRINT "John";CHR$(10);"William"
would generate the following:
John
William
Reverse Line Feed
The reverse line feed code causes the paper in the printer to be
reversed by 1/6 of an inch. The following statement,
100 LPRINT "John";CHR$(27);CHR$(10);"William"
would result in the following output:
William
John
Atari Printers 259
Half-line Feed & Reverse Half-Line Feed
The half-line feed control code causes the paper in the printer to
be advanced by 1/12 inch.
These control codes are very useful when printing subscripts. For
example, the following program line,
100 LPRINT "8";CHR$(27);CHR$(28);"10";
CHR$(27);CHR$(30);"Base Ten"
would output:
Carriage Return
8-|q Base Ten
When the carriage return code is received, the printer will return
to the left margin, and an automatic line feed will be generated.
For example, the following program line,
100 LPRINT "JOHN";CHR$(13);"WILLIAM"
would generate the following output:
JOHN
WILLIAM
Underlining
The SI code causes the underlining of characters to begin. When
an SO code is received, the underlining is discontinued. For
example, the following program line,
100 LPRINT CHR$(15);"UNDERLINE";CHR$(14);" STOP"
would generate the following output:
UNDERLINE STOP
260 User's Handbook to the Atari 400/800 Computers
Standard, Condensed, and Proportionally Spaced Character Sets
The default character set used on the Atari 825 is the standard
character set— where 10 characters per inch are output. By
sending the condensed character control code, the condensed
character set will be active. In the condensed character set, 16.7
characters per inch are output. The character width is the
uniform for all characters within either the standard (10 dot
spaces per character) or the condensed (9 dot spaces per
character) character set.
In the proportionally spaced character set, characters are
assigned different widths. For example, an I would be assigned a
more narrow width than a W. However, all digits are assigned
uniform widths. Digits will be printed at 12.5characters per inch.
Approximately 14 non-digit charactersare output per inch in the
proportionally spaced character set.
Condensed and proportionally spaced characters can be mixed
in the same output line. However, characters printed with the
standard character set cannot be mixed on the same line with
condensed or proportionally spaced characters.
The maximum line length on the Atari 825 printer is 8 inches.
Therefore, a full line of standard characters would contain 80
characters. A full line of condensed characters would contain
132 characters.
The ESC SO Code causes characters to be printed by the Atari 825
as extended or double width characters. The ESC SI code will end
extended character printing. Extended character printing also
will end when a carriage return code is encountered.
If double wide characters are being output, 40 standard
character set double wide characters would fill a line. 66
condensed double wide characters would fill a line.
Backspace & 1-6 Dot Spaces
The Backspace character code consists of the code BS followed
by the number of dot spaces (nn) to be backspaced. The BScode
Atari Printers 261
can appear as either control-H or CHR$(8). The number of
spaces can appear as a CHR$ function or as a print character or
control code. For example,
LPRINT CHR$(8);CHR$(100)
would backspace by 100 dots.
If nn (number of dot spaces) is specified as a print character or
control code, that character code's ASCII decimal equivalent
will be used as the number of dots to be backspaced. This
number can be from to 127 inclusive.
If d (with an ASCII decimal equivalent of 100) was substituted for
CHR$(100) in our previous example,
LPRINT CHR$(8);"d"
the result would still be backspacing of 100 dots.
In the standard character set, each character is considered to be
10 dot spaces wide. In the condensed character set, each
character is considered to be 9 dot spaces wide. Therefore, BS10
would backspace one character in the standard character set,
and BS 9 would backspace one character in the condensed
character set.
In the proportionally spaced character set, the number of dot
spaces per character varies from 6 to 18. The number of dot
spaces for the width of the 96 ASCII print characters is given in
Table 8-2.
The dot spacing control characters as listed in Table 8-1 can be
used to add or delete dot spaces between words and/or
characters. If dot spaces are added, the line will be extended. By
replacing the current number of dot spaces between words
and/or characters with a lesser number, the line will be
condensed.
Dot spacing can be useful in printing characters in a bold
typeface.
262 User's Handbook to the Atari 400/800 Computers
Table 8-2. Dot Space Width of Proportionally Spaced
ASCII Print Character Set
ASCII Print
Decimal
No. of
ASCII Print
Decimal
No. of
Character
Code
Dot Spaces
Character
Code
Dot Spaces
SP
32
7
O
79
16
!
33
7
P
80
14
"
34
10
Q
81
14
(t
35
15
R
82
15
$
36
12
S
83
12
%
37
16
T
84
14
&
38
14
U
85
15
39
7
V
86
16
(
40
7
W
87
18
)
41
7
X
88
16
•
42
12
Y
89
16
+
43
12
Z
90
10
44
7
1
91
12
-
45
12
A
92
12
46
7
I
93
12
/
47
12
\
94
12
48
12
95
12
1
49
12
V
96
7
2
50
12
a
97
12
3
51
12
b
98
12
4
52
12
c
99
10
5
53
12
d
100
12
6
54
12
e
101
12
7
55
12
1
102
10
8
56
12
g
103
12
9
57
12
h
104
12
58
7
i
105
8
;
59
7
i
106
6
<
60
12
k
107
12
=
61
12
1
108
8
>
62
12
m
109
16
[
63
12
n
110
12
@
64
14
o
111
12
A
65
16
P
112
12
B
66
15
q
113
12
C
67
14
r
114
10
D
68
16
s
115
12
E
69
14
I
116
10
F
70
14
u
117
12
C
71
16
V
118
12
H
72
16
w
119
16
I
73
10
X
120
12
I
74
14
y
121
12
K
75
16
z
122
10
L
76
14
{
123
10
M
77
18
1
124
7
N
78
16
I
125
10
126
12
CHAPTER 9.
ATARI GRAPHICS & SOUND
Introduction
In this chapter, we will provide an overview of the various
graphics and sound capabilities that are available in Atari BASIC.
The following commands are used to create graphics in Atari
BASIC:
GRAPHICS LOCATE PUT/GET
COLOR PLOT SETCOLOR
DRAWTO POSITION XIO
These commands will be discussed in the following sections.
GRAPHICS
The GRAPHICS command is used to select one of the 9 graphics
modes available in Atari BASIC. GRAPHICS is used with the
following configuration,
GRAPHICS X
whereX is a real numericconstant, variable, or expression which
when rounded evaluates to a positive integer.
Generally, the GRAPHICS statement will clear the video display
upon execution. However, by adding 32 to the value of X, this
display clearing function will be disregarded.
GRAPHICS
The characteristics of the various Atari graphics modes are given
in Table 9-1.
264 User's Handbook to the Atari 400/800 Computers
Table 9-1.
Atari Graphics Modes
Graphic
No. of
No. of
Mode
Mode
No. of
Rows
Rows
No. of
RAM
Number
Type
Columns
(Split Screen)
(Full Screen)
Colors
Requirement
TEXT
40
24
1*
993
1
TEXT-
20
20
24
5
513
2
TEXT
20
10
12
5
261
3
GRAPHICS
40
20
24
4
273
4
GRAPHICS
80
40
48
2
537
5
GRAPHICS
80
40
48
4
1017
6
GRAPHICS
160
80
96
2
2025
7
GRAPHICS
160
80
96
4
3945
8
GRAPHICS
320
160
192
1*
7900
"1 color; 2 luminances
Mode is the text mode. This is the standard mode that is
encountered upon power-on.
Modes contains a 24 by 40 character screen. The left margin is
set by default to column 2, and the right margin is set to column
39. These settings allow 38 characters per line. The left and right
margins can be altered by POKEing a new location to the
memory locations which specify these margins.
The left margin memory address is known as LMARGN and is
address 82. The right margin memory address is known as
RMARGN and is address 83.
In Graphics Mode 0, only one color is available in the display
area. However, 2 different levels of luminance (brightness) are
available. The color of the characters will be the same as that of
the background. However, the luminance of the characters can
differ, making them readable.
Atari Graphics & Sound 265
Upon start-up in Graphics 0, the display area color is blue (color
register 2), and the border area color is black (color register 4).
However, by changing the default values of these color registers,
the border area and display area color can be altered. This
changing of the color registers can be accomplished with the
SETCOLOR statement. For example, the following SETCOLOR
statement would change the display area from blue to orange.
SETCOLOR 2, 2, 4
The SETCOLOR statement can also be used as shown in the
following example to alter the background from black to green.
SETCOLOR 4, 12,
The concepts of color registers and the use of SETCOLOR to
change color registers will be discussed in the next section.
Color Registers & SETCOLOR
Color registers are memory locations within the Atari which set
the foreground, background, and border colors. The Atari
contains 5 color registers. These are numbered from through 4
inclusive. The Atari's operating system uses the following RAM
addresses to store the current color in each register.
Address Name Address Location Color Register No.
COLOR0 Address 708 Color Register
COLOR1 Address 709 Color Register 1
COLOR2 Address 710 Color Register 2
COLOR3 Address 711 Color Register 3
COLOR4 Address 712 Color Register 4
Each of the 5 color registers has a default color defined. These
default values are listed in Table 9-2.
The default color values for the 5 color registers can be changed
with the SETCOLOR command. SETCOLOR uses the following
configuration:
SETCOLOR register*, color*, luminance*
266 User's Handbook to the Atari 400/800 Computers
Table 9-2. SETCOLOR Register Default Values
SETCOLOR Default Luminance
Register No. Color No. Value
1
2
3
4
2
12
9
4
8
10
4
6
Actual
Color
Orange
Green
Dark Blue
Pink
Black
Thereg/sfer# indicates the number of the register whose default
values are to be altered. The colorti indicates the color to which
the register indicated is to be set. The sixteen available colors are
listed in Table 9-3 with their associated SETCOLOR numbers.
The luminance indicates the brightness value of the color.
Luminance can range from (darkest) to 14 (brightest). Odd
luminance values give the same luminance as the next lowest
even value. By combining the different color and luminance
values, as many as 128 different shades of color can be created.
Table 9-3. Atari Colors and Color Numbers
Color
Color
Color
Number
Color
Number
Gray
Blue
8
Gold
1
Light Blue
9
Orange
2
Turquoise Blue
10
Red
3
Green Blue
11
Pink
4
Green
12
Violet
5
Yellow-Green
13
Blue Purple
6
Orange-Green
14
Blue
7
Orange
15
Atari Graphics & Sound 267
GRAPHICS 1 & 2
Graphics Modes 1 and 2 are both text modes. The items available
for display can be chosen from either of two 64 character sets.
The standard character set consists of the upper case letters,
digits, and punctuation symbols. The alternate character set
consists of the lowercase letters and special graphics characters.
The standard character set will be active whenver the Atari is
powered on, the System Reset key is pressed, or when a
GRAPHICS statement is executed. By executing the following
statement,
POKE 756,226
the alternative character set can be selected. If the statement,
POKE 756,224
is subsequently executed, the standard character set will again
be active. Table 9-4 lists the characters in the standard and
alternative character sets along with their COLOR statement
color register values (explained later in this chapter).
In Graphics mode 1, the characters are printed at the same
height as those specified in Graphics mode 0. However, they are
printed at twice the width as the characters in Graphics 0. In
Graphics mode 2, the characters are printed at both twice the
length and twice the height as the characters in Graphics mode 0.
Graphics modes 1 and 2 use what is known as a split screen
display (see Illustration 9-1). The split screen consists primarily of
a graphics window with 4 lines of text displayed at the bottom of
the display.
In the split screen mode, a PRINT statement will cause data to be
displayed in the text window. A PRINT #6 statement causes data
to be output to the graphics window.
The split screen can be changed to a full graphics screen by
adding 16 to the graphics mode number.
268 User's Handbook to the Atari 400/800 Computers
Table 9-4. Standard & Alternative Character Sets in
Graphics Modes 1 and 2 and Color Register Values
Value for
Character
Color
Register
Std. Alt.
1
2
3
s
32*
160
128
!
T
33
1
161
129
"
J
34
2
162
130
T
.i
35
3
163
131
I
r
36
4
164
132
%
5_
37
5
165
133
A
7"
38
6
166
134
I
\
39
7
167
135
I
4
40
168
136
2
■
41
9
169
137
T
E
42
10
170
138
+
B
43
11
171
139
eT
44
12
172
140
-
™
45
13
173
141
46
14
174
142
$
■
47
15
175
143
0.
*
48
16
176
144
J_
_F
49
17
177
145
2
50
18
178
146
_L
i
51
19
179
147
T
«^
52
20
180
148
T
~
53
21
181
149
T
L
54
22
182
150
j_
=r-
55
23
183
151
_8
3;
56
24
184
152
2.
r
57
25
185
153
&.
58
26
186
154
',
\
59
27
187
**
<
i
60
28
188
156
=
±
61
29
189
157
>
^
62
30
190
158
T
~
63
31
191
159
*155 will designate the same character and color register as 32.
**No value is available to select this color register/character.
Atari Graphics & Sound 269
Table 9-4 (Cont.). Standard & Alternative Character Sets
in Graphics Modes 1 and 2 and Color Register Values
Character
Std. Alt.
11
2
A
a
B
b
C
r
D
(1
E
g
F
I
L
&
H
LL
[II
i
J
i
K
k
1
i
M
m
N
n
O
n
Ltd
JjJ
P
dJ
r
r
s
s
1
t
I J
II
V
y
w
vv
X
X
bJ
L
z
z
I
I
L_
I
1
^
A
J
B
Value for
Color Register
1
64
65
66
67
192
193
194
195
96
97
98
99
68 100 196
69 101 197
70 102 198
71 103 199
72 104 200
73 105 201
74 106 202
75 107 203
76 108 204
77 109 205
78 110 206
79 111 207
80 112 208
81 113 209
82 114 210
83 115 211
84 116 212
85 117 213
86 118 214
87 119 215
88 120 216
89 121 217
90 122 218
91 123 219
92 124 220
93
221
94 126 222
95 127 223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
"No value is available to select this color register/character.
270 User's Handbook to the Atari 400/800 Computers
Illustration 9-1. Split Screen Display
(Row = 0)
(Column = 0)
S: (device)
Graphics Window
Column Position (graphics or text)
Row
Position
Border
E: (device)
Text Window
(4 lines)
Five different default colors are available in graphics modes 1
and 2. These correspond to color registers through 4 (see Table
9-2).
Color register 4 controls the background and border colors. The
default color is color with a luminance of 0. This sets the
background and border colors to black. The following
SETCOLOR statement,
SETCOLOR 4,0,4
would set the border and background colors to grey in graphics
modes 1 and 2. SETCOLOR 4,2,4 would set the background and
border colors to orange.
In graphics modes 1 and 2, the color of the characters output in
the graphics window depends on the type of character. The
color registers and default colors used for each type of character
are summarized in Table 9-5.
Atari Graphics & Sound 271
Table 9-5. Default Color Registers For Characters
Entered in Graphics Modes 1 and 2
Type of Character
Color
Register
Default Color
Upper Case Alphabetic
Inverse Upper Case Alphabetic
Lower Case Alphabetic
Inverse Lower Case Alphabetic
Numbers
Inverse Numbers
2
1
3
2
2 - Orange
9 - Dark Blue
12 - Green
4 - Red
2 - Orange
9 - Dark Blue
By executing a SETCOLOR statement, the characters will be
output using the colors specified in SETCOLOR. For instance, if
the following statement was executer in graphics modes 1 or 2,
READY
GRAPHICS
PRINT #6; "9.
j press ,/|v. key
1"
i press vf.key a second time
the number 9 would be displayed in dark blue in the graphics
window.
If the following SETCOLOR statement was subsequently
executed,
READY
SETCOLOR 2, 1,6
the number 9 would be changed from dark blue to gold.
Subsequent inverse number entries also would be output in
gold.
In graphics mode 0, it is not possible to draw lines or plot points.
In graphics modes 1 and 2, lines can be drawn with the DRAWTO
statement and points plotted with the PLOT statement. The use
of these statements will be discussed later in this chapter. First,
however, the use of the COLOR statement will be discussed.
272 User's Handbook to the Atari 400/800 Computers
COLOR Statement in Graphics Modes 0, 1, and 2
The COLOR statement determines the color register to be used
with subsequent PLOT or DRAWTO statements. In graphics
modes 0,1, and 2, COLOR also specifies the character which will
be output by subsequent PLOT or DRAWTO statements.
COLOR is used with the following configuration,
COLOR numericexp
The value of numericexp along with the current graphics mode
will determine the color register number used.
Table 9-6 can be used to determine the color register number
from the COLOR statements numericexp value and the current
graphics mode. For example, if a COLOR 3 statement was
executed in graphics mode 7, SETCOLOR register number 2
would be used for by subsequent PLOT and DRAWTO
statements.
In graphics mode 0, the items displayed are characters—not
points. In graphics mode 0, the COLOR statement will specify
the character to be displayed by subsequent DRAWTO and
PLOT statements. Table 9-7 includes the values to be used with
the COLOR statement to generate the character desired in
graphics mode 0.
For example, the following statement,
GRAPHICS
COLOR ASC("Y")
PLOT 10,10
will display a "Y" in screen position 10,10 in graphics mode 0.
Atari Graphics & Sound 273
Table 9-6. Determination of SETCOLOR Register
From COLOR Statement in Graphics Modes 3 Through 8*
Graphics Modes 3, 5, 7
SETCOLOR
Register Number
COLOR numericexp
Value
1
2
3
4
1
2
3
Graphics Modes 4, 6
SETCOLOR
Register Number
COLOR numericexp
Value
1
2
3
4
1
*ln graphics modes 0, 1, and 2, the argument of COLOR
determines the character to be displayed by PLOT or DRAWTO.
274 User's Handbook to the Atari 400/800 Computers
Graphics Mode 8*
SETCOLOR
Register Number
COLOR numericexp
Value
1
2
3
4
1
**ln graphics mode 8, the color used will always be specified by
SETCOLOR register 2. Only the luminance can be altered in
graphics mode 8. (See Page 292).
Atari Graphics & Sound 275
Table 9-7. Characters Displayed by COLOR
Statement Values in Graphics Mode
COLOR Value
COLOR Value
COLOR VALUE
Character
Normal/Inverse
Character
Normal/Inverse
Character
Normal/Inverse
^_^
▼
0/128
n
35/163
1
70/198
T
1/129
±_
36/164
c
71/199
J
2/130
37/165
H
72/200
*
3/131
£
38/166
l
73/201
I
4/132
39/167
J_
74/202
!_
5/133
j
40/168
k
75/203
/
6/134
1
41/169
1
76/204
C=3
\
7/135
•
42/170
M
77/205
I
8/136
T~
43/171
N
78/206
■
9/137
44/172
O
79/207
E
10/138
_
45/173
P
80/208
—%
11/139
46/174
£
81/209
T~
12/140
47/175
_K_
82/210
=
13/141
48/176
l -
83/211
14/142
1
49/177
J_
84/212
■
15/143
)
50/178
L
85/213
*
16/144
)
51/179
V
86/214
¥
17/145
4
52/180
w
87/215
™
18/146
5
53/181
X
88/216
S
19/147
6
54/182
_v_
89/217
■
20/148
~~
55/183
/
90/218
21/149
~
56/184
z
91/219
L
22/150
~
57/185
92/220
^*
23/151
58/186
]
93/221
ib
24/152
59/187
T
94/222
c
25/153
<
60/188
95/223
L
26/154
~~
61/189
7
96/224
?
~
27/—
62/190
.i
97/225
i
28/156
>
63/191
j_
98/226
1
29/157
T
64/192
(
99/227
.*.
30/158
■\
65/193
d
100/228
~
_».
31/159
66/194
e
101/229
32/160
T~
67/195
1
102/230
=
33/161
O
68/196
_y_
103/231
34/162
1
69/197
TT
104/232
276 User's Handbook to the Atari 400/800 Computers
Table 9-7 (cont.) Characters Displayed by COLOR
Statement Values in Graphics Mode
COLOR Value
COLOR Value
COLOR Value
Character
Normal/Inverse
Character
Normal/Inverse
Character
Normal/Inverse
1
105/233
106/234
s
114/242
115/243
ffi
123/251
124/252
k
T
til
107/235
108/236
109/237
i
u
V
116/244
117/245
118/246
cl
scrn
E
I
125/ —
126/254
127/255
n
110/238
w
119/247
EOL
— /155
P
111/239
112/240
X
V
120/248
121/249
□
— /253
<!
113/241
7.
122/250
The COLOR statement works in much the same fashion in
graphics modes 1 and 2. However, there are two important
differences in the use of the COLOR statement in graphics
modes 1 and 2 as opposed to graphics mode 0.
First of all, two different character sets can be displayed— the
standard character set and alternative character set. These are
depicted in Table 9-4. The standard character set is active upon
power-on, when the System Reset key is pressed, or when a
GRAPHICS statement is executed. POKE 756,226 will select the
alternate character set, while POKE 756,224 will return to the
standard character set.
The second major difference between the use of the COLOR
statement in graphics mode 1 and 2 and graphics mode is that in
graphics mode 1 and 2, the characters can be produced using
SETCOLOR registers 0, 1, 2, or 3. This makes it possible to
produce each character using any one of four different colors.
Notice in Table 9-4 that different COLOR statement parameters
are used to select the SETCOLOR register.
Atari Graphics & Sound 277
For example, if the following statements were executed,
GRAPHICS 2
COLOR 159: PLOT 5,5
DRAWTO 5,0
a question mark would be displayed in row 5, column 5 of the
graphics window when the PLOT statement is executed. Upon
execution of the DRAWTO statement, a column of six question
marks will be output from row 5, column 5 on the screen to row
0, column 5.
PLOT
The PLOT statement is used in graphics modes 3 through 8 to
display a point on the graphics window. PLOT uses the following
configuration,
PLOT column, row
where column gives the column position and row gives the row
number. The color of the point being plotted will be determined
by the color register specified by the most recent COLOR
statement. If no COLOR statement had been executed since the
computer was powered on, the point will be displayed by the
PLOT statement in the background color register.
Although PLOT is generally used in graphics modes 3 through 8,
it can also be used in graphics modes 0, 1, and 2. In modes 0, 1,
and 2, a character rather than a point is plotted on the screen.
In graphics mode 0, the numeric expression specified with the
last COLOR statement will determine the characterdisplayed by
PLOT. In graphics modes 1 and 2, the last COLOR statement will
choose both the character displayed by PLOT and the color
register to display that character. The numeric expression used
with COLOR will be 0, if a COLOR statement had not been
executed prior to the PLOT statement.
278 User's Handbook to the Atari 400/800 Computers
DRAWTO
The DRAWTO statement is used to draw a straight line from the
last point displayed by a PLOT statement or another DRAWTO
statement to the point given as its argument.
DRAWTO uses the following configuration,
DRAWTO column, row
where column and row specify the screen position where the
line is to be drawn to.
The line will be drawn in the color register specified by the last
COLOR statement. If no COLOR statement had been previously
executed, the background color will be used.
Although DRAWTO is generally used in graphics modes 3
through 8, the statement can also be used in graphics modes 0,1,
and 2. In these modes, the line drawn will consist of characters
rather than points.
In graphics modes 1 and 2, the numeric expression specified with
the last COLOR statement will determine the character used to
compose the line as well as the color register used for the line
color. In graphics modeO,thenumericexpression specified with
the last COLOR statement will determine just the character used
to compose the line.
COLOR will be used by default to determine the character (and
color) if a COLOR statement had not been executed since the
computer had been turned on.
Graphics Modes 3 Through 8
In graphics modes 3 through 8, points, lines, and solid areas are
displayed as opposed to characters. The number of lines on the
display screen, number of points per line, point size, and
number of color registers available differs among modes 3
through 8. These differences are summarized in Table 9-8.
Atari Graphics & Sound 279
Graphics modes 3, 5, and 7 normally have split screen displays.
However, the display can be changed from split-screen to full
screen by adding 16 to the graphic mode number when the
GRAPHICS statement is executed.
Graphics modes 3, 5, and 7 each have 4 color registers available
(registers 0, 1, 2, and 4). Color register4 controls the background
and border colors. The foreground colors are controlled by
registers 0, 1, or 2. Color register 3 is unused in graphics modes 3,
5, and 7.
In graphics mode 3, the split-screen is divided into 20 rows of 40
columns each. In graphics mode 5, the screen is divided into 40
rows of 80 columns each. In graphics mode 7, the screen is
divided into 80 rows of 160 columns each.
Table 9-8. Summary of Graphics Modes Features
Mode
No. of
No. of Rows
No. of
RAM
No.
Columns
Split Screen
Full Screen
Color Registers
Required
40
.
24
1
993
1
20
20
24
5
513
2
20
10
12
5
261
3
40
20
24
4
273
4
80
40
48
2
537
5
80
40
48
4
1017
6
160
80
96
2
2025
7
160
80
96
4
3945
8
320
160
192
1
7900
Graphics modes 4 and 6 have one foreground color register and
one background and border color register. Even though modes
4 and 6 have the same number of rows and columns as modes 5
and 7 respectively, less RAM is required for modes 4 and 6.
280 User's Handbook to the Atari 400/800 Computers
This is due to the fact that modes 4 and 6 are two-color modes,
while modes 5 and 7 are four-color modes. One bit per graphics
point is required in a two-color mode, while two bits per point
are required in a four-color mode. For this reason,
approximately one-half as much memory is required in graphics
modes 4 and 6 as in modes 5 and 7 respectively.
Graphics mode 8 results in a screen of 160 rows by 320 columns in
split screen and 192 rows by 320 columns in full screen. This is the
highest resolution available in Atari graphics.
In graphics mode 8, the background/border color register
controls the color the graphics points displayed on the screen.
Although the foreground color cannot be selected, the
luminance of the foreground color register can be set.
Using the COLOR Statement in Graphics Mode 8
In graphics mode 8, the background color as well as all points
and lines plotted on it use color register 2 to determine the color.
Color 9 (light blue) is the default value in color register 2. The
default color can be altered by executing a SETCOLOR
statement as shown in the following example.
READY
GRAPHICS 8
SETCOLOR 2,2,8
By executing the preceding SETCOLOR statements, the
background color in graphics mode 8 is changed from light blue
to orange.
When used in graphics mode 8, the COLOR statement does not
determine the color of any points or lines plotted on the
screen. Only the luminance of the lines and points is affected.
With a COLOR value of 0, any points or lines will be displayed in
color register 2. The color and luminance of the points and lines
plotted will match the color and luminance of the background.
Therefore, these points and lines will not be visible when they
are plotted.
Atari Graphics & Sound 281
With a color value of 1, any points or lines will be displayed with
the luminance value specified in color register 1 and the color in
color register 2. In other words, the luminance of the points and
lines is affected by the execution of a COLOR 1 statement, but
the color used remains the same as the background color.
The following series of statements illustrate the use of the
COLOR statement in graphics mode 8.
100 GRAPHICS 8
110 COLOR 1
120 PLOT 50,50: DRAWTO 100,100
RUN
When the preceding statements are executed, a series of points
will be plotted from position 50,50 to 100,100 with a luminance
value of 10. These points will be discernable to the naked eye
on the video display.
If the following program lines were then added,
NEW
100 COLOR
110 DRAWTO 60,60
RUN
a series of points would be plotted from position 100,100 to
60,60 with a luminance value of 4. Since this is the same
luminance as that of color register 2 (which was set by the
COLOR statement), the points plotted would be invisible to
the naked eye.
POSITION
Although the graphics cursor is invisible in graphics modes 3
through 8, it can still be moved with the POSITION statement.
POSITION is used with the following configuration,
POSITION column, row
where column and row specify the screen column and row
282 User's Handbook to the Atari 400/800 Computers
numbers to which the cursor is to be moved. The next PRINT,
PUT, GET, INPUT, or LOCATE statements will use this cursor
position. However, DRAWTO, PLOT, and XIO will not use the
new cursor position specified by POSITION.
The cursor will not actually move until a subsequent input or
output command to the screen has been issued.
LOCATE
The LOCATE command positions the graphics cursor to the
position specified and returns the code corresponding to the
character or point displayed at that position. LOCATE is used
with the following configuration.
LOCATE column, row, code
row and column specify the screen location, code must be a
numeric variable. The value returned from the position specified
is assigned to the numeric variable named in code.
The code returned by LOCATE is interpreted in the same
manner as the codes used with the COLOR statement. In
graphics mode 0, this code specifies the character being
displayed. Use Table 9-7 to interpret the code returned by
LOCATE in graphics mode 0.
In graphics modes 1 and 2, the code indicates both the character
and the color register used todisplaythat character. Use Table 9-
4 to interpret the code returned by LOCATE in graphics modes 1
and 2.
In graphics modes 3 through 8, the code returned by LOCATE
identifies the color register in use at the position specified. Use
Table 9-6 to interpret the code returned by LOCATE in graphics
modes 3 through 8.
When LOCATE is used to read a code from the screen, the cursor
will move one location to the right. If the cursor was on the last
column of a row when LOCATE was executed, the cursor may
Atari Graphics & Sound 283
attempt to advance to the first column of the next row resulting
in Error 141 (Cursor Out of Range).
LOCATE moves the cursor by altering the values stored in
memory address 84 (current cursor row number) and memory
addresses 85 and 86 (current cursor column number). The cursor
position change as a result of the execution of LOCATE will have
no effect on DRAVVTO and XIO statements, as they use memory
addresses 90, 91, and 92 to determine the next cursor address.
PUT (Graphics)
The PUT statement can be used in the graphics modes to display
a character or point. PUT uses the following configuration in
graphics.
PUT #6, code
code specifies a character in graphics modes through 2. In
graphics modes 3 through 8, code specifies a color register.
When PUT outputs data to the screen, memory addresses 84
(next cursor row number) and addresses 85 and 86 (next cursor
column number) are incremented. When a subsequent
statement that outputs data to the screen or sends data to it is
executed, the cursor will advance by one position.
PUT's updating of the next cursor addresses will not affect
subsequent DRAWTO or XIO statements as these use different
cursor position memory addresses (90, 91, and 92).
If PUT is executed with the cursor in the last column of a row, the
cursor will attempt to advance to the first position of the next
row. If this occurs, error 141 (Cursor Out of Range) may appear.
XIO (Graphics)
XIO is used in graphics to fill an area of the screen. XIO uses the
following configuration.
XIO command, channel #, numexpl, numexp 2, device
284 User's Handbook to the Atari 400/800 Computers
command specifies the type of XIO command to be executed.
The XIO commands are listed in Table 5-4. The command for XIO
fil I area is 18. The channel# specified must be opened for input or
output. In graphics, channel 6 is used, numexpl and numexp 2
are given dummy values (0) unless XIO is used in conjunction
with an RS-232 operation or to open a channel, device refers to
the input or output device used with the XIO command. The
device specified for XIO when used as a fill area command in
graphics will be "S:".
The following example illustrates the use of the XIO command to
fill an area in graphics.
XIO Example Program
100 GRAPHICS 5
200 COLOR 1
300 PLOT 50,20
400 DRAWTO 50,10
500 DRAWTO 10,10
600 POSITION 20,20
700 POKE 765,1
800 XIO 18,#6,0,0,"S:"
The following steps must be followed in the order specified in
order to fill an area on the graphics display.
1. PLOT the point at the bottom right-hand corner of the
figure to be filled. (Reference line 300 in the XIO Example
Program).
2. Execute a DRAWTO to the upper right-hand corner of the
figure. (Reference line 400 in the XIO Example Program).
3. Execute a DRAWTO to the upper left-hand corner of the
figure (Reference line 500 in the XIO Example Program).
4. Execute a POSITION statement to move the cursor to the
lower left-hand corner of the figure (Reference line 600 in
XIO Example Program).
Atari Graphics & Sound 285
5. Execute a POKE to address 765. The argument specified
with POKE should be set equal to the COLOR statement
that was used to plot the points and lines. (Reference line
700 in XIO Example Program).
6. Execute XIO 18,#6,0,0,"S:" and the figure will be filled.
(Reference line 800 in the XIO Example Program).
Atari Sound
The Atari's built-in speaker is controlled via memory address
53279. When a is stored at that address, an oscillation is sent to
the speaker. By causing the speaker to oscillate a number of
times, the speaker will emit a sound. The following program will
result in the Atari's speaker emitting sounds.
READY
100 FOR I = 1 TO 100
200 POKE 53279,0
300 NEXT I
400 END
RUN
Generally, the television set's speaker is used to produce sound
rather than the Atari's built-in speaker. In Atari BASIC, the
SOUND statement is used to output sound via the television set's
speaker.
The SOUND statement is used with the following configuration.
SOUND voice, pitch, distortion, volume
Together these four arguments determine the sound produced.
voice sets one of four voices available with the Atari. These are
numbered from to 3. These four voices are independent of
each other. In other words, as many as four voices can be
sounded at the same time.
pitch sets the pitch of the sound produced by the SOUND
statement. The pitch can range from to 255. The highest pitch
begins at and the lowest at 255.
286 User's Handbook to the Atari 400/800 Computers
The SOUND statement can produce either pure or distorted
tones, distortion can range between and 15. A distortion value
of 10 or 14 will produce a pure tone. Any of the other even
distortion values (0, 2, 4, 6, 8, 10, and 12) will generate a different
amount of noise into the tone produced. The amount of this
noise will depend upon the distortion and pitch values specified.
The odd numbered distortion values (1,3, 5, 7, 9, 11, 13) cause the
voice indicated in the SOUND statement to be silenced. If the
voice is on, an odd-numbered distortion value will result in its
being shut off.
The volume controls the loudness of the voice indicated in
SOUND, volume ranges from (no sound) to 15 (highest
volume).
An Atari BASIC statement with a volume of will turn off the
sound. Sound can also be turned off by executing an END, RUN,
NEW, DOS, CSAVE, or CLOAD. If the System Reset key is
pressed, sound will be turned off. However, if the Break key is
pressed, sound will not be turned off.
Appendix A. 287
Appendix A. Atari Error Messages
This appendix describes the error numbers used by the Atari.
Error numbers 2 through 21 should only occur when a BASIC
program is being run. Error numbers 128 through 173 result from
errors in the usage of input/output devices such as disk drives or
printers.
Error
#
Error Name
Insufficient Memory
Value Error
Too Many Variables
String Length Error
Out of Data Error
Cause & Recovery
Additional memory is required to
store the statement or to dimension
the new string variable. By adding
more RAM or by deleting any
unused variables, this error can be
avoided. This error can also be
caused by including a FOR-NEXT
statement with too many levels of
nesting.
A numeric value was encountered
that was outside of the allowed
range i.e. too largeortoosmall.This
error can also occur when a nega-
tive value is returned when the
value should be positive.
Over 128 variable names have been
specified. Any unused names
should be deleted.
The program attempted to read or
write outside of the range for which
the string was dimensioned. This
also occurs when zero is used as the
index. This error can be corrected
by increasing the DIM index size.
The DATA statements did not con-
tain enough data items for the vari-
ables in the corresponding READ
statements.
288 User's Handbook to the Atari 400/800 Computers
Error
#
Error Name
Cause & Recovery
7
Line Number Greater
The line number is negative or
Than 32767
greater than 32767.
8
INPUT Statement Error
An attempt was made to input a
non-numeric value into a numeric
variable. Be certain that the type of
data being entered corresponds to
the INPUT variable type.
9
Array or String
This error occurs when the program
DIM Error
references an array or string which
has not been dimensioned. This
error also occurs when a DIM state-
ment includes a string or array that
was previously dimensioned.
10
Argument Stack
An expression is too large or there
Overflow
too many GOSUB statements.
11
Floating Point
The program encountered a num-
Overflow/Underflow
ber with an absolute value less than
1E-99 or greater than 1E+98. This
error also occurs when an attempt is
made to divide by zero.
12
Line Not Found
An IF-THEN, ON-GOSUB, ON-
GOTO, GOSUB, or GOTO state-
ment referenced a line numberthat
does not exist.
13
No Matching FOR
A NEXT statement was encountered
that did not have a corresponding
FOR statement.
14
Line Too Long
The line entered is greater than the
length of the BASIC line processing
buffer length.
15
GOSUB or FOR
A NEXT or FOR statement was en-
Line Deleted
countered for which the corres-
Appendix A. 289
Error
#
Error Name
Cause & Recovery
ponding FOR or GOSUB statement
had been deleted.
16
RETURN Error
A RETURN statement was en-
countered without a corresponding
GOSUB statement.
17
Garbage Error
This error can be caused by faulty
RAM or the incorrect use of a POKE
statement.
18
Invalid String
A string does not begin with a valid
Character
character or the argument of a VAL
statement is not a numeric string.
19
LOAD Program Too
The program being loaded will not
Long
fit in the available RAM.
20
Device Number Error
A device number outside of the
range to 7 was entered.
21
LOAD File Error
The LOAD statement was incor-
rectly used to load a program saved
by CSAVE or ENTER.
128
BREAK Abort
The Break key was pressed during
an I/O operation causing execution
to stop.
129
IOCB* Already Open
This error occurs when an attempt is
made to use a channel currently in
use. Often, the channel causing the
error is automatically closed.
130
Nonexistent Device
This error occurs when a program
attempts to access a device which is
undefined. This error can occur
when a filename is given without a
required device name (ex. "FILE.-
BAS" instead of "D:FILE.BAS").
*IOC!
3— Input/Output Contro
Block
290 User's Handbook to the Atari 400/800 Computers
Error
#
Error Name
Cause & Recovery
131
IOCB Write Only
An attempt was made to read from a
file opened only for write oper-
ations. The file must be reopened
for a read or read/write operation.
132
Invalid Command
This error is generally caused by an
illegal command code being used
with an XIO or IOCB command.
133
Device/File
A channel was referenced before it
Not Open
was opened.
134
Bad IOCB
An attempt was made to use an il-
Number
legal IOCB index. A BASIC program
can only use channels 1-7.
135
IOCB Read
An attempt was made to write to a
Only Error
device or file that isopened only for
read operations.
136
End of File
The end-of-file record was reached.
137
Truncated Record
This error occurs when an attempt is
made to read a record whose record
size is larger than the allowed maxi-
mum. This error also occurs when
an INPUT statement is used to read
from a file created with a PUT
command.
138
Device Timeout
The external device specified does
not respond within the time al-
lowed by the Atari operating sys-
tem. Be certain the proper device
was specified, the device is properly
connected, and that the device's
power is on.
139
Device NAK
The device does not respond, as it
received an incorrect parameter.
Check the input/output command
Appendix A. 291
Error
#
Error Message
Cause & Recovery
for any illegal parameters. Also, be
certain all cables are properly
connected. This error can also result
when the Atari 850 Interface
Module is unable to accept five, six,
or seven bit input at an excessive
baud rate.
140
Serial Frame Error
This is a very rare error. If this error
reoccurs, have the computer and/
or devices checked.
141
Cursor Out of Range
The cursor is outside the defined
limits for the current graphics
mode. This error can be corrected
by using legal cursor positioning
parameters.
142
Serial Bus Overrun
This error is due to serial bus data
problems. If the error reoccurs, the
disk unit, cassette unit, or computer
may require service.
143
Checksum Error
The communications on the serial
bus are in error. The problem may
be due to either defective hardware
or faulty software.
144
Device Done Error
This error is generally due to an
attempt to write to a write-pro-
tected diskette or device.
145
Read. After-write
The disk drive identified a differ-
compare Error or
ence between what was written and
Bad Screen Mode
what should have been written.
Handler
Also, this error can result from a
problem with the screen handler.
146
Function Not
An attempt was made to use a de-
Implemented
vice in a manner not allowed (ex.
write to the keyboard).
292 User's Handbook to the Atari 400/800 Computers
Error
#
Error Message
Cause & Recovery
147
Insufficient RAM
More RAM is required for the
graphics mode chosen. Either add
RAM or change graphics modes.
150
Port Already
An attempt was made to open a
Open
serial port already open.
151
Concurrent Mode
Before current mode input/output
I/O Not Enabled
is enabled with the XIO 40 state-
ment, the serial port must have
been opened for concurrent mode.
152
Illegal User
Upon the initialization of the con-
Supplied Buffer
current input/output, an incorrect
buffer length and address was used.
153
Active Concurrent
An attempt was made to access a
Mode I/O Error
serial port while another serial port
was open and active in the con-
current mode.
154
Concurrent Mode
The concurrent mode must be
I/O Not Active
active for the input/output oper-
ation to be executed.
160
Drive Number
The specified drive must be D:, D1 :,
Error
D2:, D3:, or D4:. This error can also
be caused if the drive was not
powered on or if a drive buffer was
not specified.
161
Too Many Open
Another file may not be opened, as
Files
the limit of open files has been
reached. Generally, only 3 disk files
can be open at the same time.
162
Disk Full
All diskette sectors are in use.
163
Unrecoverable
Either the DOS or the diskette con-
System I/O Error
tains an error. Try using a different
DOS diskette.
Appendix A. 293
Error
#
Error Message
Cause & Recovery
164
File Number
The POINT statement moved the
Mismatch
file pointer to a sector which was
not included in the open file. This
error can also occur when the file's
intra-sector links are incorrect.
165
File Name Error
The filename is illegal. Check the
file specification.
166
POINT Data
The POINT statement attempted to
Length Error
move to a byte number that did not
exist within the specified sector.
167
File Locked
An attempt was made to write to, re-
name, or erase a locked file.
168
Device Command
An attempt was made to use an il-
Invalid
legal device command.
169
Directory Full
A diskette directory's maximum
capacity is 64 filenames.
170
File Not Found
An attempt was made to access a file
not present in the disk directory.
171
POINT Invalid
The POINT statement was used with
a disk sector in a file not opened for
Update.
172
Illegal Append
An attempt was made to open a
DOS I fileforappend using the DOS
II operating system. Try copying the
DOS I file to a DOS II diskette using
DOS II. It is illegal for DOS II to
append to DOS I files.
173
Bad Sectors at
Bad sectors were found while the
Format Time
disk drive attempted to format the
diskette. A diskette with bad sectors
cannot be formatted. Use another
diskette.
294 User's Handbook to the Atari 400/800 Computers
Appendix
B. Atari BASIC Reserved Words
Reserved
Reserved
Word
Abbrev.
Word
Abbrev.
ABS
NEXT
N.
ADR
NOT
AND
NOTE
NO.
ASC
ON
ATN
OPEN
O.
BYE
B.
OR
CLOAD
CLOA.
PADDLE
CHR$
PEEK
CLOG
PLOT
PL.
CLOSE
CL.
POINT
P.
CLR
POKE
POK.
COLOR
C.
POP
COM
POSITION
POS.
CONT
CON.
PRINT
PR. or ?
COS
PTRIG
CSAVE
CS.
PUT
PU.
DATA
D.
RAD
DEG
DE.
READ
REA.
DIM
Dl.
REM
R. or .
DOS
DO.
RESTORE
RES.
DRAWTO
DR.
RETURN
RET.
END
RND
ENTER
E.
RUN
RU.
EXP
SAVE
S.
FOR
F.
SETCOLOR
SE.
FRE
SGN
GET
GE.
SIN
GOSUB
GOS.
SOUND
SO.
GOTO
G.
SQR
GRAPHICS
GR.
STATUS
ST.
IF
STEP
INPUT
1.
STICK
INT
STRIG
LEN
STOP
STO.
LET
LE.
STR$
LIST
L.
THEN
LOAD
LO.
TO
LOCATE
LOC.
TRAP
T.
LOG
USR
LPRINT
LP.
VAL
NEW
XIO
X.
Appendix C. 295
Appendix C. Atari ASCII Code Set
In this appendix, the 256 characters in the standard character set
of graphics mode are listed along with the Atari ASCII codes for
each character. The keystrokes used to produce the characters
are also listed along with the associated standard ASCII character
(if any). Remember, in graphics modes other than graphics
mode 0, an entirely different character may be output.
Some of the Atari ASCII codes produce control characters.
When control characters are output using a PRINT statement,
nothing is actually displayed on the screen. When control
characters are output with a PRINT statement, a control process
of some kind will be executed or the cursor will be moved.
Control characters can be included in PRINT statements by
supplying the CHR$ function with the Atari ASCII code of the
control character. Control characters can also be output by using
an escape sequence enclosed within quotation marks.
To produce an escape sequence, first press the Escape key, and
then press the keys which will produce the desired control
character. For example, if the Escape key is pressed prior to
pressing the Control key and the = key, the Atari ASC code 29 for
cursor down is produced.
When an escape sequence is used with a control character, the
control process does not actually take place during keyboard
entry. However, the control character does appear on the
screen. When the PRINT statement containing the escape
sequence and control character is executed,the control process
will take place.
For example, if the following statement was entered,
READY i ESC\CTRL-+
PRINT "NNN— A" pressed here
296 User's Handbook to the Atari 400/800 Computers
The output produced would be;
NNA
Notice that when the ESC\CTRL-+ keyboard entry was made,
the control process specified (cursor left) did not actually occur.
However, the screen character for cursor left (—) was displayed
on the screen.
When the PRINT statement was subsequently executed, the
cursor left control process did take place. The result of this
control process was the movement of the cursor one position to
the left (over the third N entry) and the display of the A in place
of the previous character entered (N).
If the Atari ASCII code 27 (keyboard entry ESC\ESC) is included
in the PRINT statement just before the control character, that
control process will not occur. However, the control character
will be displayed.
For example, if the following statement was entered,
i ESC \ ESC pressed here
PRINT "NNNEt— A"
* ESC\CTRL-+ pressed here
the following output would be displayed on the screen;
NNN^A
Notice that while the control process did not occur, the control
character was displayed.
A great number of the Atari characters can only be entered via
the keyboard when the keyboard is in the lower case mode. By
pressing the LOWR key once, the keyboard will be in the lower
case mode. If the CAPS key is pressed (SHIFT-LOWR keys), the
keyboard is returned to the upper case mode.
Appendix C. 297
1/1 s
< %
< u
— IV
<
i «
C -o
V o
D U
Keystrokes
For Outputting
Character
fe
NULL
CTRL-,
a
SOH
1
CTRL-A
a
5TX
2
CTRL-B
a
ETX
3
CTRL-C
E
EOT
4
CTRL-D
E
ENQ
5
CTRL-E
ACK
6
CTRL-F
s
BEL
7
CTRL-G
SI
BS
8
CTRL-H
Q
HT
9
CTRL-I
IB
LF
10
CTRL-]
a
VT
11
CTRL-K
E
FF
12
CTRL-L
n
CR
13
CTRL-M
a
SO
14
CTRL-N
SI
15
CTRL-O
B
DLE
16
CTRL-P
□
DC1
17
CTRL-Q
H
DC2
18
CTRL-R
ffl
DC3
19
CTRL-S
H
DC4
20
CTRL-T
S
NAK
21
CTRL-U
E
SYN
22
CTRL-V
B
ETB
23
CTRL-W
H
CAN
24
CTRL-X
IE
EM
25
CTRL-Y
S
SUB
26
CTRL-Z
in
ESC
27
ESC/ESC
ffl
FS
28
ESC/CTRL-
m
GS
29
ESC/CTRL-=
B
RS
30
ESC CTRL-+
B
US
31
ESC CTRL-*
a
Space
32
SPACE BAR
□
|
33
SHIFT-1
□
34
SHIFT-2
£
< %
< u
5
u
— rg
iy> -C
< U
1 «
o u
Keystrokes
For Outputting
Character
#
35
SHIFT-3
$
36
SHlFT-4
m
%
37
SHIFT-5
&
38
SHIFT-6
□
39
SHIFT-7
m
(
40
SHIFT-9
□
)
41
SHIFT-0
□
•
42
•
□
+
43
+
□
,
44
□
□
-
45
46
-
□
/
47
/
48
m
1
49
1
m
2
50
2
m
3
51
3
4
52
4
m
5
53
5
m
6
54
6
m
7
55
7
8
56
8
9
57
9
□
58
SHIFT-;
59
s
<
60
<
H
=
61
=
>
62
>
!
63
SHIFT-/
@
64
SHIFT-8
A
65
A
B
66
B
C
67
C
D
68
D
E
69
E
298 User's Handbook to the Atari 400/800 Computers
£
(A S
< %
— n
| *
01
i
Keystrokes
For Outputting
< u
< u
Q U
Character
m
F
70
F
G
71
C
H
72
H
CD'
1
73
1
m
J
74
]
m
K
75
K
m
L
76
L
M
M
77
M
N
78
N
O
79
O
m
P
80
P
m
Q
81
Q
R
82
R
®
S
83
S
a
T
84
T
U
85
U
V
86
V
w
87
w
X
88
X
m
Y
89
Y
m
z
90
z
m
[
91
SHIFT-;
s
92
SHIFT-,
[i]
]
93
SHIFT-+
□
t
94
SHIFT-*
s
*-
95
SHIFT-
H
1
96
CTRL-.
13
a
97
(LOWR) A
El
b
98
(LOWR) B
c
99
(LOWR) C
d
100
(LOWR) D
e
101
(LOWR) E
f
102
(LOWR) F
g
103
(LOWR) G
h
104
(LOWR) H
5 J
< 1
< U
£
8
— 2
«
<u
■§ a
Q U
Keystrokes
For Outputting
Character
i
105
(LOWR) I
m
i
106
(LOWR) j
k
107
(LOWR) K
1
108
(LOWR) L
m
109
(LOWR) M
n
110
(LOWR) N
o
111
(LOWR) O
P
112
(LOWR) P
q
113
(LOWR) Q
r
114
(LOWR) R
s
115
(LOWR) S
t
116
(LOWR) T
u
117
(LOWR) U
V
118
(LOWR) V
w
119
(LOWR) W
X
120
(LOWR) X
y
121
(LOWR) Y
z
{
122
123
(LOWR) Z
CTRL-;
m
1
124
SHIFT-=
HE
}
125
ESC/CTRL- <
ESC/SHIFT-*
m
126
ESC/BACK S
E
DEL
127
ESC/TAB
□
128
l/W CTRL-,
D
129
(/IV) CTRL-A
D
130
VM CTRL-B
a
131
(/IM CTRL-C
a
132
(A) CTRL-D
a
133
(A) CTRL-E
□
134
(A) CTRL-F
□
135
(A) CTRL-G
B
136
(A) CTRL-H
m
137
(A) CTRL-I
i
138
(A) CTRL-J
m
139
(A) CTRL-K
Appendix C. 299
u 5
< g
m 3
< U
t
= re
< u
re
J £
QU
Keystrokes
For Outputling
Character
a
140
(A) CTRL-L
B
141
(A) CTRL-M
H
142
(A) CTRL-N
9
143'
(A) CTRL-O
□
144
(A) CTRL-P
B
145
(A) CTRL-Q
B
146
(A) CTRL-R
:;
147
(/|V) CTRL-S
□
148
(A) CTRL-T
H
149
(A) CTRL-U
11
150
(A) CTRL-V
B
151
(A) CTRL-W
B
152
lA) CTRL-X
a
153
C/|V> CTRL-Y
E
154
(A) CTRL-Z
155
RETURN
□
156
ESC/SHIFT-
BACK S
D
157
ESC/SHIFT- >
□
158
ESC/CTRL-
TAB
B
159
ESC/SHI FT-
TAB
■
160
0\\)
SPACE BAR
□
*161
(A) 5HIFT-1
□
162
(A) SHIFT-2
163
(A) SHIFT-3
164
C/IVJ SHIFT-4
165
(A) SHIFT-5
166
(A) SHIFT-6
□
167
(A SHIFT-7
□
168
(A) SHIFT-9
□
169
(A) SHIFT-0
□
170
(A)'
£
< %
si
< u
— re
(j re
(^ -e
< U
re
1 »
&* O
a u
Keystrokes
For Outputting
Character
H
171
(A) +
□
172
(A).
□
173
IAI-
□
174
<A).
□
175
(A)/
m
176
tA)0
m
177
(An
a
178
A) 2
m
179
(A) 3
180
(AH
LH
181
lA)5
LH
182
IA6
183
(#J7
184
lA)8
185
(A)9
186
(A) SHIFT-;
187
m>
s
188
(A)<
189
(A» =
a
190
(A»
191
(A! SHIFT-/
192
(Al SHIFT 8
193
(A A
194
(*»B
195
(A)C
196
(A) D
□
197
tflV) E
198
(A)F
199
(AC
200
Al H
201
(A) i
....
•All Atari ASCII characters from 161-255 inclusive are displayed in reverse.
300 User's Handbook to the Atari 400/800 Computers
< u
ftj
u
_ rQ
< u
.1 i
i
Q U
Keystrokes
For Outpulting
Character
m
202
(Ai I
E
20J
(A) K
E
204
(Al L
205
(A) M
206
(A) N
207
m o
E
208
i/top
El
209
*Q
m
210
(AR
e
211
(AS
m
212
(AT
e
213
(Ai U
E
214
C/IVJ V
215
(Ai w
B
216
(AI x
E
217
(Ai y
e
218
(Az
m
219
(Ai shift-,
E
220
(A) SHIFT-+
m
221
(A SHIFT-.
□
222
(A) SHIFT-'
□
223
lA) SHIFT-
ai
224
(A CTRL-.
h
225
(A) (LOWR) A
E
226
(A) (LOWR) B
E
227
t/JVj (LOWR) C
E
228
(A) (LOWR) D
E
229
(A) (LOWR) E
E
230
(Al (LOWR) F
E
231 '
(A (LOWR) C
E
232
(Al (LOWR) H
E
233
(A) (LOWR) I
E
234
(A (LOWR) )
E
235
(Al (LOWR) K
E
236
(A) (LOWR) L
U S"
»-
< |
E „
Keystrokes
m "1
< U
< u
-
Q U
For Outpulting
Character
E
237
(Al (LOWR) M
E
238
(A) (LOWR) N
E
239
(A) (LOWR) O
E
240
(Al (LOWR) P
E
241
(A (LOWR) Q
E
242
(A) (LOWR) R
E
243
(A) (LOWR) S
E
244
(A (LOWR) T
E
245
(A) (LOWR) U
E
246
(A) (LOWR) V
E
247
(Al (LOWR) W
E
248
(A) (LOWR) X
E
249
(A) (LOWR) Y
E
250
(A) (LOWR) Z
E
251
(A) CTRL-;
E
252
(A) SHIFT-=
H
253
ESC/CTRL-2
m
254
(A) ESC/CTRL-
BACK S
IE
255
(A)
ESC/CTRL- >
All Alari ASCII characters (rom 161-255 inclusive are displayed in reverse.
Appendix D. 301
Appendix D. Atari 400/800 Memory Map
The following illustrations and tables depict the organization of
memory in the Atari 400/800. Note that the addresses for the top
of RAM, OS, and BASIC may differ according to the amount of
memory present.
Illustration D-1. Memory Map Without BASIC
65536
57344
55296
53248
49152
40960
32768
10879
1792
Operating System ROM 1
Floating Point Routines
Hardware Registers 2
Not Used
Cartridge Slot A
Cartridge Slot B 3
RAM (8-40K)
DOS
Operating System RAM 4
302 User's Handbook to the Atari 400/800 Computers
Illustration D-2. Memory Map With Atari BASIC
65536
57344
55296
53248
49152
40960
32768
10879
1792
1 Reference Table D-1.
2 Reference Table D-2.
3 Atari 800 only.
4 Reference Table D-3.
5 Reference Table D-4.
6 Reference Table D-5.
Operating System ROM 1
Floating Point Routines
Hardware Registers 2
Not Used
BASIC ROM 5
Cartridge Slot B 3
BASIC Program Area
DOS
Operating System RAM 6
& 8K BASIC
Appendix D. 303
Table D-1. Operating System ROM Memory Addresses
Memory Address
Reference
62436-65535
Display & Keyboard Handling Routines
61667-62435
Monitor
61249-61666
Cassette Handling Routines
61048-61248
Printer Handling Routines
60906-61047
Disk Handling Routines
59716-60905
SIO
59093-59715
Interrupt Handling Routines
58534-59092
CIO
58496-58533
Initial RAM Vectors .
58448-58495
Jump Vectors J
58432-58447
Cassette Vectors / Operating
58416-58431
Printer Vectors \ System
58400-58415
Keyboard Vectors ( Vectors
58384-58399
Screen Vectors 1
58368-58383
Editor Vectors /
57344-58367
Character Set
Table D-2. Hardware Register Memory Addresses
Memory Address
Reference
54784-55295
Not Used
54272-54783
ANTIC
54016-54271
PIA
53760-54015
POKEY
53504-53759
Not Used
53248-53503
CTIA or GTIA
304 User's Handbook to the Atari 400/800 Computers
Table D-3. Operating System RAM Memory Addresses
Memory Address
Reference
1152-1791
User RAM
512-1151
Operating System RAM (detailed be
ow)
1021-1151
Cassette Buffer
1000-1020
Spare
960-999
Printer Buffer
944-959
I/O Channel 7
928-943
I/O Channel 6
912-927
I/O Channel 5
896-911
I/O Channel 4
880-895
I/O Channel 3
864-879
I/O Channel 2
848-863
I/O Channel 1
832-847
I/O Channel
794-831
Handler Address Tables
780-793
Miscellaneous
768-779
DCB
736-767
Miscellaneous
712-735
Spare
704-711
Colors
656-703
Screen RAM
648-655
Miscellaneous
624-647
Game Controllers
554-623
Miscellaneous
512-553
Interrupt Vectors
256-511
Stack
128-255
User Page RAM
0-127
Operating System Page RAM
Appendix D. 305
Table D-4. BASIC ROM Memory Addresses
Memory Addresses
Reference
48549-49151
Floating Point
47733-48548
I/O Routines
47543-47732
Graphics
47382-47542
Errors
47128-47381
CONT Subroutines
45321-47127
Execute Statement
45002-45320
Execute Function
44164-45001
Execute Operator
44095-44163
Operator Precedence
43744-44094
Execute Expression
43632-43743
Operator Table
43520-43631
Statement Table
43359-43519
Execute CONT
43135-43358
Memory Manager
42509-43134
Syntax Tables
42159-42508
Statement Name Table
42082-42158
Search
41056-42081
Syntax
41037-41055
Warm Start
40960-41036
Cold Start
Table D-5. Operating System RAM and BASIC
Memory Address
Reference
End of Free RAM-1792
BASIC Program
1536-1791
Free RAM
1406-1535
Input Line Buffer
1152-1405
Syntax Stack
512-1151
Operating System RAM
256-511
Stack
128-255
BASIC Page RAM
0-127
Operating System Page RAM
306 User's Handbook to the Atari 400/800 Computers
Appendix E. Atari PEEK and POKE Locations
This appendix lists memory addresses that BASIC programmers
may wish to access via the PEEK or POKE statements.
In BASIC, memory addresses as well as the contents at those
addresses are given in decimal notation. Each address contains a
value between and 255.
Two consecutive addresses are required to store numbers
greater than 256. In these instances, the value of the first address
plus the value of the second address multiplied by 256 will result
in the total value. For example, PEEK (97) + 256 * PEEK (98) will
return the ending graphics cursor column.
Most Atari memory locations are referred to by name as well as
by decimal memory address. Both are given in Appendix E.
Decimal
Address
Name
Description
14,15
88,89
128,129
144,145
APPMHI
SAVMSC
LOMEM
MEMTOP
Memory Addresses
These addresses contain
the highest address that can
be used for program lines
and variables.
These addresses contain
the lowest screen memory
address. The contents of
that address will be dis-
played in the screen's
upper right-hand corner.
The BASIC low memory
pointer.
The BASIC top of memory
pointer.
Appendix E. 307
741,742
MEMTOP
The highest address in the
free memory address will
be returned by PEEK (741) +
PEEK (742) * 256 - 1.
743,744
MEMLO
These locations contain the
lowest address in the free
memory area.
Screen Addresses
82
LMARGIN
This address gives the col-
umn position of the left
margin in graphics mode.
The default value is 0.
83
RMARGIN
This address gives the col-
umn position of the right
margin of the screen in
graphics mode. The de-
fault value is 39.
84
ROWCRS
This address gives the cur-
rent row position.
85,86
COLCRS
This address gives the cur-
rent column position.
87
DINDEX
This address gives the cur-
rent screen mode.
90
OLDROW
This address specifies the
starting graphics cursor row
for DRAWTO and XI018
statements.
91,92
OLDCOL
This address gives the be-
ginning graphics cursor
column for DRAWTO and
XIO 18 statements.
308 User's Handbook to the Atari 400/800 Computers
93
OLDCHR
This address contains the
character beneath the cur-
sor. This value will be used
to redisplay the character
when the cursor is moved.
94,95
OLDADR
This address contains the
current text cursor address.
This value is used with
address 93 to restore the
character beneath the cur-
sor once the cursor is
moved.
96
NEWROW
This address contains the
ending cursor row for a
DRAWTO or graphics XIO
statement.
97,98
NEWCOL
This address contains the
ending cursor column for a
DRAWTO or graphics XIO
statement.
201
PTABW
This address indicates the
number of columns be-
tween tab stops. The de-
fault value is 10.
656
TXTROW
This address indicates the
cursor row in the text win-
dow. This value will range
from to 3, with indi-
cating the top row in the
text window.
Appendix E. 309
657,658
TXTCOL
This address indicates the
cursor column in the text
window. This value will
range from to 39, with
being the first column.
752
CRSINH
A value of at this address
results in the cursor not
being visible. Any other
value results in the cursor
being visible.
755
CHACT
This address generally hasa
value of 2. Any other
value will result in the cur-
sor's being opaque, the
cursor being absent, or
characters being inverted.
These values and their ef-
fect are summarized in
Table E-1.
756
CHBAS
This address indicates the
character set to be used in
graphics modes 1 and 2 (224
= standard; 226 = alternate).
763
ATACHR
This address contains the
Atari ASCII code for the last
character read or written or
last graphics point output.
765
FILDAT
The address containsthefill
data to be used with a
graphics XIO command.
1
Graphics Addresses
708
COLOR0
Color register 0.
310 User's Handbook to the Atari 400/800 Computers
709
COLOR1
Color register 1.
710
COLOR2
Color register 2.
711
COLOR3
Color register 3.
712
COLOR4
Color register 4.
Cassette Buffer
61
BPTR
This address contains a
pointer to the next location
to be accessed in the cas-
setted buffer.
63
FEOF
If this address contains a 0,
an end-of-file has not been
encountered. A value of
indicates an end-of-file has
been encountered.
649
WMODE
This address indicates the
present cassette operation
(0 = read; 128 = write).
650
BUM
This address indicates the
size in bytes of the cassette
buffer (0-128).
1021-
CASBUF
These addresses are used as
1151
the cassette buffer.
Printer Addresses
29
PBPNT
This address contains a
pointer to the current loca-
tion in the printer buffer.
Appendix E. 311
30
PBUFSZ
This address indicates the
size of the printer buffer (40
= normal mode; 29 = side-
ways mode).
960-999
PRNBUF
These addresses are avail-
able for the printer buffer.
Keyboard Addresses
17
FJRKKEY
This address indicates that
the Break key has been
pressed (0 indicates Break
pressed).
694
INVFLG
This address controls
whether keyboard entries
result in normal or inverse
video character output (0 =
normal; non-zero = in-
verse).
702
SHFLOK
This address indicates
whether the caps or control
locks are in effect (0 = nor-
mal—no locks; 64 = caps
lock; 128 = control lock).
764
CH
This address contains the
value of the key which was
previously pressed. If no
key was pressed, the ad-
dress will contain 255.
53279
CONSOL
Executing a PEEK to this
location returns a value
which indicates whether a
special function key has
been pressed. These values
along with the function key
indicated are listed in Table
E-2.
312 User's Handbook to the Atari 400/800 Computers
POKE (53279,8) retracts the
core of the built-in speaker
while POKE (53279,0)
extends it. When these two
statements are alternated,
clicking sounds will be
emitted from the speaker.
Miscellaneous
65
186,187
195
212,213
251
SOUNDR
STOPLN
ERRSAV
FRO
RADFLG or
DEGFLG
If the value for this address
is 0, sound can be heard
over the television set dur-
ing disk or cassette access-
ing. A value of eliminates
this sound.
These addresses return the
line number where exe-
cution of a BASIC program
was stopped due to a STOP
statement, a TRAP state-
ment, an error, or the
Break key being pressed.
This address contains the
error number if an error
takes place.
These addresses contain a
value which is to be re-
turned to a BASIC pro-
gram from a USR function.
This address determines
whether trigonometic
functions are calculated
using degrees or radians (0
= radians; 6 = degrees).
Appendix E. 313
Table E-1. Address 755 Values and Effects on
Cursor and Character Display
Address 755
Cursor
Cursor
Characters
Value
Visible/Not Visible
Transparent/Opaque
Normal/Inverse
Not Visible
Transparent
Normal
1
Not Visible
Opaque
Normal
2
Visible
Transparent
Normal
3
Visible
Opaque
Normal
4
Not Visible
Transparent
Inverted
5
Noi Visible
Opaque
Inverted
6
Visible
Transparent
Inverted
7
Visible
:
Opaque
Inverted
Table E-2. PEEK (53279) Function Key Values
Value
Returned
Function Keys Pressed
OPTION, SELECT, & START
1
OPTION & SELECT
2
OPTION & START
3
OPTION
4
SELECT & START
5
SELECT
6
START
7
None
Index 315
INDEX
ABS 92
AC Power Adapter 10, 11
ADR 92
Alternative Character Set 276
AND 56, 57. 58, 92, 93, 94
Append Operation 225
Argument 74
Arithmetic Expressions 51, 54
Arithmetic Operators 53
Arrays 49, 50, 51
Arrow Keys 34
ASC Function 78, 94
ASCII 75
ASCII Code Set 295, 297, 298, 299, 300
Assignment Statements 60
Atari 400 7, 8, 9
Atari 400. Installation 21
Atari 410 Program Recorder 9, 14, 15.
147, 163. 189
Atari 800 7, 8. 9
Atari 800, Installation 19
Atari 810, Installation 21, 22, 23
Atari 810 Disk Drive 10, 15, 16, 148. 163
205
Atari 820 Printer 10, 11. 149, 164, 253
Atari 820 Printer, Installation 23
Atari 822 Printer 16, 149, 164, 253
Atari 822 Printer, Installation 24
Atari 825 Printer 16, 17, 149, 164, 253
Atari 825 Printer, Installation 24, 25
Atari 830 Modem 17
Atari 850 Interface Module 16. 17. 24
25. 152. 165
Atari ASCII 75, 78
Atari ASCII Code Set 295, 297, 298, 299
300
Atari ASCII Format 192, 193
Atari BASIC 9, 37
Atari Educational System 9
Atari Key (JR.) 34
Atari Keyboard 11, 148
ATN 94, 95
Auto Repeat Key 36
AUTORUN.SYS 215
Back S Key 35
Backspace, Printer 260
BASIC, Atari 9, 37
BASIC Reserved Words 294
BASIC ROM Cartridge
Binary Load 236. 237
Binary Save 234, 235, 236
Blocks 192, 197, 201
Boolean Expression 51
Boolean Operations 53, 56, 57
Booting, DOS 217, 218
Branching Statements 68, 69
Break Key 32, 72, 73
Buffer, Cassette 198
Buffer, Disk 217, 247, 248, 250
BYE 95
Bytes 13
C: 147, 163, 167
Caps Key 33, 296
Caps/Lowr Key 33
Carriage Return 259
Carriage Return/Line Feed 63
316 User's Handbook to the Atari 400/800 Computers
Cartridges, ROM 25
Cassette Buffer 198, 201
Cassette Tape 189
Chaining 197, 243
Channel 145, 162, 166, 169
Channel, I/O 145
Channel Switch 10
CHR$ 78, 96, 254, 258, 261
Clear Key 35
CLOAD 83, 95, 96, 104, 174, 190, 192
193, 194
CLOG 96
CLOSE 97, 198, 200, 246, 247
CLR97
COLOR 98, 99, 100, 101, 102, 137, 156,
267, 272, 273, 274, 275, 276, 277, 278
280, 281
Color Registers 100, 265, 26, 272
COM 102, 103
Comma, Formatting 63
Compound Expressions 52
Concatenation 77
Condensed Character Set 260
Conditional Statements 68
Constants 47
CONT Command 32, 72, 73, 103, 180
Control Characters 256, 295, 296
Control Key 33
Controller Jacks 10
Copy File 223, 225, 226, 227
COS 104
Create MEM.SAV 238, 239
CSAVE 83, 95, 104, 190, 191, 192,
193, 194
Cursor Control 86
D: 147, 148, 149
DATA 60, 61, 62, 105, 106, 170, 171, 172
Data blocks 198
Data Files 189, 190, 244
Default 222
DEG 106, 107, 169
Delete File 227, 228
Delete Key 35
Delimiter 61
Density 15
Device Names 146, 147, 199
Device Timeout Error 147
DIM 49, 50, 51, 102, 107, 108, 109
Directory Full Error 224
Disk Buffer 217, 247, 248, 250
Disk Directory 220
Disk Drive 10, 15, 16
Disk Files 213
Disk Full Error 224
Diskettes 205, 207, 208
Diskettes, Double-Sided 15, 211
Diskettes, Single-Sided 15, 211
Display Lines 41
DOS 110, 111, 215, 216, 218
DOS 1.0 110, 111, 215, 216,218
DOS 2.0 110, 111, 215, 216, 218
DOS Menu 110, 111, 218, 219, 220
DOS.SYS111,216
Dot Spaces, Printer 260, 261, 262
Double-Sided Diskettes 211
Down Arrow Key 34
DRAWTO 99, 112, 113, 138, 139, 151
161, 272, 278, 283
Duplicate Diskette 233, 234
Duplicate File 239, 240, 241
E: 147, 150
Editor 149, 150
ELSE 68
END 40, 73, 74, 114
END Parameter 235
ENTER 114, 115, 134, 136, 174, 190, 192
193, 194, 242, 243
EOF Record 198
EOL Character 84, 85, 201, 202, 203, 248,
249, 255
Error Mesages 43, 287, 288, 289, 290
291, 292, 293
Error Traps 91
ESC Key 36, 79
Escape Sequence 36, 79, 80, 86, 295, 296
Execution, Program 40, 41
EXP 115, 116
Exponentiation 54
Expressions 51, 52
Fields 189, 190
File Management Subsystem 211
File Not Found Error 224
Filename Extension 213, 214
Index 317
Filename Match Characters 213, 214
Filenames 213
Files 189, 213
Floating Point Decimal 44
Floppy Diskettes 207, 208
FOR 66, 67, 68. 116, 117, 118. 141, 142
Format Diskette 232
Formatting 232
FRE 118
From Paramter 223
Functions 74
Game Controls 17
GET 119, 120, 121 ,122, 123, 197. 200, 202
203, 244, 248, 250
GOSUB 69, 70, 71, 72, 123, 124, 159, 160
172
GOTO 42, 69, 70, 125, 126
GRAPHICS 101, 126, 137, 151, 263
Graphics Characters 80, 81, 82
Graphics Mode 263, 264, 275
Graphics Mode 1 267, 268, 269, 270
271, 273
Graphics Mode 2 267, 268, 269, 270
271, 273
Graphics Modes 3,5,7 273, 278, 279,
280
Graphics Modes 4,6 273, 278, 279, 280
Graphics Mode 8 274, 278, 280
Graphics Window 270
Half-Line Feed 259
Hard Disks 205, 206
Hard Sectors 209, 210
Hardware Stack 183, 184
Home 87
I/O Channel 145. 162, 166. 199, 246
I/O Operations 145, 146, 245, 246
IF THEN 68, 90. 126, 127, 128
Immediate Mode 37
Index Hole 209, 210
Index Variable 67
INIT Address 235, 236
INPUT 64, 65, 129, 130, 131, 132
INPUTS 197, 200, 202, 203, 244, 248, 249
250
Input Error Checks 89, 90
Input Programming 88
INPUT Prompt 65, 66
Insert Key 35
INT 132, 133
Integers 44
Interpreters 18
(oysticks 17, 178, 179
K: 147, 148
Keyboard, Atari 11, 20
Keyboard Controllers 17
Keywords 41, 42. 148
Kilobytes 14
Languages 18
Leader 198
Left Arrow Key 34
LEN 77, 133
LET 47, 60, 133, 134
Line Feed 258
Line Numbers 38, 39
LIST 40, 42, 114, 134. 135, 136, 190, 191,
192, 193, 194, 240, 242
List File 221, 222
LIST P: 253
Listing, Program 42
LOAD 136, 137, 190, 192, 193, 194, 242,
243
Loading 189
LOCATE 137, 138. 139, 282, 283
Lock File 230, 231
LOG 139
Logical Operators 56, 57
Loops 66, 67
Loops, Nested 67
LOWR Key 33, 296
LPRINT 63, 64. 139. 140. 145, 254, 255
Megabyte 205
Memo Pad Mode 25, 110
Memory Addresses 301 through 313
MEM:SAV 111, 215, 224, 238, 239
Merging 224
Modem 17
Modulo 202, 248
Monitor 11, 12
Monitor, Installation 13
Monochromatic Text Mode 12
318 User's Handbook to the Atari 400/800 Computers
Nested Loops 67
NEW 40, 83, 136, 140, 141, 143, 193
NEXT 66, 67, 68, 116, 117, 118, 141, 142
NOT 56, 57, 58, 142
NOTE 143, 216, 250
Numeric Data 43, 44
ON GOSUB 72, 90, 124, 144, 159, 172
ON GOTO 70, 90, 125, 144, 145
OPEN 97, 119, 120, 121, 122, 129, 130,
131, 132, 145, 146, 147, 148, 149, 150,
151, 152, 163, 164, 165, 166, 198, 199,
244, 245, 246
Operands 51
Operating System 9, 17, 18
Operators 51
Option Key 31
OR 56, 57, 58, 153, 154
Order of Evaluation 53
P: 147, 253
PADDLE Function 154, 155
Paddles 17, 154, 155
Parameters 41
PEEK 83, 87, 155
Pixel 101
PLOT 98, 101, 102, 112, 113, 151, 156,
157, 161, 272, 277, 278
Plug-In Cartridges 13
POINT 157, 158, 215, 250, 251
POKE 83, 84, 88, 155, 158, 159, 276
POP 159, 160, 172
POSITION 84, 87, 160, 161, 281, 282
Power On 26, 27, 28. 29
PRINT 42, 62, 63, 84, 161, 162, 163, 164,
165, 295, 296
PRINT* 197, 200, 201, 244, 247, 248, 255
Print Zone 63
Printer Buffer 255
Printer Character Sets 255, 260
Printer Control Characters 256, 257,
258
Program Execution 41
Program Files 190
Program Lines 41
Program Listing 42
Program Mode i7, 38
Program Recorder 9, 14, 15
Program Recording Formats 191
Programs, Applications 18
Prompt Messages 65, 66, 88, 89
Proportional Character Set 260, 262
PTRIG 166
PUT 166, 167, 168, 169, 197, 200, 202,
244, 247, 248, 255, 283
R: 152
RAD 169
RAM 14, 83
Random Access 205
READ 60, 61, 62, 105, 106, 109, 170, 171
Read/Write Head 205
Reading 189. 248
READY Message 29, 37
Records 189, 190, 191
Relational Expression 51
Relational Operations 53, 55
REM 59, 60, 171
Remark Statements 59
Rename File 228, 229, 230
Reserved Words 41, 294
RESTORE 61, 62, 170, 171, 172
RETURN 71, 123, 172
Return Key 32
Reverse Half-Line Feed 259
Reverse Line Feed 258
Right Arrow Key 34
RND 172, 173
ROM 14
ROM Cartridges, Installation 25, 26
Rounding 46
RUN 37, 173, 174, 243
RUN Address 235, 236
Run At Address 237, 238
RUN C: 195, 196, 197
Run Cartridge 22, 223
S: 147, 150, 164
SAVE 95, 137, 173, 174, 190, 191 , 240, 241
SAVE C: 174, 191
Saving Programs 189, 190, 240
Scientific Notation 45, 46
Screen I/O Operations 151
Screen Margins 88
Search Spec 221, 222
Index 319
Sectors 208, 209 TAB Function 85
Select Key 32 Tab Key 35. 85
Semicolon, Formatting 63 Tab Stops 85, 86
SETCOLOR 100, 101, 175, 265, 266, 271, Tables 49, 50
273, 280 Television Set, Display 11, 12
Sequential Access 205 Television Set, Installation 11, 12
SGN 175 Text Data 43
Shift Key 32 TO Parameter 223. 224
Simple Expression 52 Tokenized Format 192
SIN 175, 176 Tracks 208, 209
Single-Sided Diskettes 211 TRAP 91, 181. 182
Soft Sectors 209, 210, 211 TV Switch Box 9, 11, 19, 20
Software 17
SOUND 176. 177, 285, 286 Unary Operation 54
SQR 74, 177 Underlining. Printer 259
Standard Character Sets 260, 276 Unlock File 231
Start Key 31 Up Arrow 34
START Parameter 235 USR 182,
Statement 41
STATUS 177 VAL 183, 184
STATUS Codes 178 Variable Names 48
STEP 67, 141, 142 Variable Name Table 82, 83, 193, 194
STICK 178 Variable Storage 82
STOP 73, 180 Variables 47
STR$ 181 Variables, String 48, 49
STRIC 179 Video Display 11
String Concatenation 77
String Handling 76 Winchester Disk 205, 206
String Variables 49. 50 Write DOS 213, 232
Strings 43 Writing 189
Subroutines 70, 71
Subscript 49, 50 XIO 138, 139, 161, 184, 185, 187, 188,
Subscripted Variables 49, 50 283. 284. 285
Substrings 76
System Reset Key 31, 72, 73
$13.95
USER'S HANDBOOK TO THE ATARI 400/800® COMPUTERS
The User's Handbook to the Atari 400/800® Computers is a
clear, concise, and practical guide to the capabilities and
operation of the Atari 400 and 800 computers, as well as the '
various Atari peripherals and expansion devices.
A complete description of the Atari 400 and 800 computers,
Atari 410 Program Recorder, Atari 810 Disk Drive, Atari 850
Interface Module, and the Atari 820, 822, and 825 Printers is
included. A step-by-step guide to the set-up, operation,
maintenance, and programming of the Atari 400 and 800 is
also offered.
The following topics are covered in detail:
Atari Installation
Plug-In Cartridges
Atari Power-On Sequence
Atari Keyboard Usage
Atari BASIC Programming
Using Atari DOS
Atari 410 Program Recorder Usage
Atari 810 Disk Drive Usage
Atari Printer Usage
Atari Graphics
Atari Sound
Atari BASIC Reference Guide
No user or potential user of the 400 or 800 computer should
be without the User's Handbook to Atari 400/800 Computers.
NV3I
WEBER
SYSTEMS
INCORPORATED
LC: 82-051088
ISBN: rj-T3AAbZ-15-M
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